Subject: Well when should I take my pool cover off??!!

From: [email-masked] (John Harrison)
Date: Sat, 05 Oct 1996 20:55:57 GMT

There has been a bit (?!) of ranting on this topic here.
I am still not sure of the facts about solar blankets for the pool.
This is all theoretical as I haven't got one yet!!
Obviously I leave it on at night. 
When the sun comes up and starts to warm the air, ground, and water at
what point should I take the cover off to let the rays do their work
directly on the water, or does the evaporation ALWAYS suck out more
energy then can be provided directly (meaning I only take the cover
off to actually swim!)
Is there some quirky relationship between air temp and water heat
transfer that will enable me to know when its beneficial to take the
cover off at other times?
Please keep responses prettty simple - I don't wann be playing with
the cover more than twice a day if possible (on and off!!!)

---

From: [email-masked] (Ken Tait)
Date: Sun, 06 Oct 1996 19:56:24 GMT

>There has been a bit (?!) of ranting on this topic here.

That's an understatement!!  I agree with you totally and hope this
reply does not bring on the rath of god (NP) (PS- the small "g" is not
a typo.)  I have been following this group for a year now and frankly
have been intimidated to such a point that I thought it best not to
participate.  Well here goes!

>This is all theoretical as I haven't got one yet!!

If you have a pool, GET A BLANKET!
If you havn't got a pool, when you do install one, heat it with solar
>from  the beginning.

>Obviously I leave it on at night. 

Yes an no!  Bad answer I know, but I'll touch on this at the end.

>energy then can be provided directly (meaning I only take the cover

The heat load or loss on a pool is affected by many variables.  Water
temp., air temp., ground temp., water table level, humidity, wind
speed, construction of pool, type of pool (above, on or in ground)
etc., etc.

And of course most of these are changing varibles depending on time of
day, time of season, climate, weather etc.  So its quite clear, there
is no real answer to your question.  Common sense will have to
prevail.

A pool blanket reduces heat loss by   A) reducing evaporation.
 and   B) reducing heat transfer out of the water (to the air)

A pool blanket reduces heat GAIN by   C) Shading the pool.

So take the blanket off when you think all the variables are in your
favour and will remain that way more or less, for a period of time.

Examples:  Assume pool is at 80F.
	Its raining and cloudy		-on
	Its sunny, warm and no wind	-off
	Its sunny, cool and dry and windy	-on
	Its sunny, hot and humid, but thunder
	 showers called for all afternoon 	-God knows?

>cover off at other times?

Now the answer to your first assumption. --"Blanket on at night".

A side effect of a pool blanket is that it screws up the water flow in
the pool, particularly at the surface.  This causes stagnant areas
that breed algae and bacteria.  Bubble pack covers are the worst for
this.  Leaving the blanket on all the time is not good!!!
Also taking the cover off and on and off and on........
is a real PAIN.

So another judgement call.  If you leave the cover off at night you
will lose tons of heat.  I mean tons, were talking millions of BTU's.

You will either have a cold unusable or at least unpleasant pool if
you dont heat it, or a costly proposition if you heat it with oil,
gas, elec. 

However if your smart and heat it with solar, who cares if the cover
is off or not.  The heat you lose at night will go back in the pool
costing you nothing, limiting the algea problems and reducing the
cover on, off, on, off--you know what I mean-- problem.  Additional
advantages are that you wear out the cover less and it will last
longer and of course all the tons of heat are now in your pool and not
in your attic so if you have AC your saving again.  When the variables
are such that the loss is bigger than you can gain during the day,
start using the cover.

>the cover more than twice a day if possible (on and off!!!)

I hope this was simple because it sure was long---sorry about that.

Ken Tait, P. Eng.
President
Heliocol Canada Inc.
http://www.sunsolar.com

---

From: [email-masked] (Nick Pine)
Date: 7 Oct 1996 01:09:25 -0400

>... hope this reply does not bring on the rath of god (NP)...

He (God) is a Merciful God, but He does not Suffer Fools Gladly.
Especially They who Purveyeth, and Acteth as if they Knoweth,
but Knoweth Not, and Will Not Accepteth Truth.

>I have been following this group for a year now and frankly have been 
>intimidated to such a point that I thought it best not to participate.

Welcome to the group :-) I've been told it can be a good idea to keep one's
mouth closed and not reveal one's ignorance. I'm still learning about this.

>>I am still not sure of the facts about solar blankets for the pool.
 
Perhaps you have been talking with experts?

>Yes an no! 

Yes, I'd suggest. But hey, I'm not an solar pool expert.

>>energy then can be provided directly

I'd guess that almost always happens.

>(meaning I only take the cover off to actually swim!)

Good idea.

>speed, construction of pool, type of pool (above, on or in ground)
 
Since you are a P. Ing, Ken, perhaps you could easily come up with a
precise calculation indicating when it would make sense to leave an
R1 transparent pool cover off the pool, when the sun is shining.

>is no real answer to your question.

>From  a thermal point of view, it's clear to me: unless the pool is too hot,
leave the cover on, except for swimming. With insignificant exceptions.
Also I'm beginning to think that solar pool experts can't spell.
Do solar pool experts have Silly Walks (tm) too?

>Common sense will have to prevail.

And perhaps a little arithmetic?

>A pool blanket reduces heat loss by   A) reducing evaporation.

Enormously, in most cases. Here's one version of a formula for the ratio
of heat loss by convection to the heat loss by evaporation, for a pond,
independent of windspeed, from page 664 of Duffie and Beckman's 1991
_Solar Engineering of Thermal Processes_:

Qc   0.001(Tp-Ta)     where Tp and Ta are pond and ambient temps (F) and
-- = ------------           Pwp and Pa are vapor pressures at the pond
Qe     Pwp - Pa             surface and ambient vapor pressure in inches
                            of mercury, 29.6" being 1 atmosphere. 

What else? Clausius-Clapeyron: ln Vp = 17.863-9621/Tabsolute,
and humidity ratio W = 0.62198 Pw/(P-Pw). And Qe is roughly 
(Tp-Ta)(2+V/2) Btu/hr-ft^2 with a windspeed of V mph. And a
clear sky can suck heaps o' radiative heat out of a pool.

>and   B) reducing heat transfer out of the water (to the air)

About as much as a single pane window reduces heat loss from a house,
for small temperature differences, ie not much, as we have discussed. 

>A pool blanket reduces heat GAIN by   C) Shading the pool.

It might "shade" the pool by reflecting and absorbing 10% or 20% of the sun
that falls on the cover, depending on the color (blue being a stupid color,
I'd guess) and glazing thickness and material. Some of the reflected solar
power is lost to the sky, and some eventually ends up in the pool, likewise
absorbed power. So we might take the pool cover off when the sun is shining
if we believed that the increased gain (30 Btu/hr-ft^2, ie 10% of the peak
solar input?) would be more than the 1 Btu/hr-ft^2-F increased loss by R1
conduction and evaporation (which might be much more than that.) 

>Examples:  Assume pool is at 80F.

With what air temp (80 F?) and humidity ratio (0.0133, like Philadelphia,
in July?), and how much sun, and clouds and wind? Lacking more numbers,
this example doesn't make much sense to me.

>	Its raining and cloudy		-on

Is the air warmer than the pool? Does it rain much when it is not cloudy? 
Are there people in the pool? ("Look out, here comes Ken, trying to save
more Btus..." :-)

>	Its sunny, warm and no wind	-off

This would hardly ever make sense, I'd guess. 

>	 showers called for all afternoon 	-God knows?

God might say:

         Leave the Cover Off, If the RH is 100%, and
	 the air is at least as Warm as the Pool.
         And get out of Eden, for Dumbth.

>>cover off at other times?

I think so, but it seems to me that doesn't matter,
since those conditions hardly ever happen...

>Now the answer to your first assumption. --"Blanket on at night".

"A No-Brainer," God might say, muttering something about Earthworms
being able to Figure THAT Out, and wondering why He gave us ASCII.

>this.  Leaving the blanket on all the time is not good!!!

Perhaps the answer to this is 5 parts per billion of Cu ion, via a smidge of
CuSO4 in the water (which turns blonde hair green in larger quantities, and
causes human death in larger ones) or an Aqua-Air Cu/Ag ion electrolyzer,
((410) 489-5288) or a small air bubbler under the cover. (God: "And Don't
Pee in the Pool.")

>will lose tons of heat.  I mean tons, were talking millions of BTU's.

Unless it's a warm humid night, in which case the pool might gain heat.
Millions of Btus, even, on a Really Hot Night.

>you dont heat it, or a costly proposition if you heat it with oil,

Or a solar pool heater?

>is off or not.

Right, who cares, if it's solar heat! Solar heat is special heat. It never
leaves the pool! Solar Btus are different from oil or gas Btus. They are
special permanent Btus. And commercial solar pool heaters are inexpensive,
and they will make you feel ecological _all over_!

>The heat you lose at night will go back in the pool costing you nothing,

Solar is truly magical! Pool size, weather, covers, none of those matter,
if you have enough solar pool heaters! Now where was that order form...?

>limiting the algea problems and reducing the
>cover on, off, on, off--you know what I mean-- problem. 

Right...

>Additional
>in your attic so if you have AC your saving again.

Makes perfect sense.

>When the variables

That almost makes sense...

>I hope this was simple because it sure was long---sorry about that.

It was a long response, Ken, but it was also obtuse. 

Nick

---

From: [email-masked] (Nick Pine)
Date: 7 Oct 1996 09:01:32 -0400

God (big G) replied via god (NP), assuming He wasn't making this up:

>...Here's one version of a formula for the ratio of heat loss by convection
>to the heat loss by evaporation, for a pond, independent of windspeed, from
>p 664 of Duffie and Beckman's 1991 _Solar Engineering of Thermal Processes_:
 
>                            of mercury, 29.9" Hg being 1 atmosphere. 

If Tp > Ta, it looks like we have heat loss by convection and evaporation,
since Pa has to be less than Pwp, since the pool surface air is saturated
with water, and warmer air can hold more water than colder air, right?

When should we take the pool cover off on a day in October in Phila, with an
average temp of 56.4 F, daily min, 46.4, daily max, 66.3, record min, 35,
record max, 96 F, average humidity ratio, 0.007, and average 1020 Btu/ft^2/d
of sun that falls on a horizontal surface, if the pool temp were 80 F?

On an average day, we might take off the cover and gain 30 Btu/ft^2/hr of
solar heat, at noon, and lose (80-66.3)1ft^2/R1 = 13.7 Btu/hour by conduction.
Pwp(80F)=exp(17.863-9621/(80+460)) = 1.079" Hg, or 1.033 from page 6.4 of the
1993 ASHRAE HOF, and Pa=29.921/(1+0.62198/0.007) = 0.333" Hg, so we'd lose
1000(1.079-0.333)/(80-66.3) = 54.45 times more heat by evaporation than by
convection, ie another 746 Btu/hr-ft^2, losing a total of 760 Btu/hr-ft^2
and gaining 30 Btu/hr-ft^2, maybe, for a total loss of 730 Btu/hr. We might
evaporate 3/4 lb of water per hour per square foot of pool this way. We might 
be able to evaporate 500 gallons of water, if we did this over an 8 hour
average October day with a 24'x36' pool. So it looks like this strategy won't
work very well in Phila, on an average October day.

How close would the air temp have to be to the pool temp, to make it worth
taking the "solar pool cover" off? Looks like the breakeven point is when 

30 = (80-Ta)(1+1000(exp(17.863-9621/(Ta+460))-0.333)), or 
   = (80-Ta)(333-1000(exp(17.863-9621/(Ta+460)), ignoring convection,
   = 26640 - 80,000 exp(...) - 333 Ta + 1000 Ta exp(...), or
   = 26640 - 333 Ta - 1000(80-Ta)exp(17.863-9621/(Ta+460)), or

Ta - 3(80-Ta)exp(17.863-9621/(Ta+460)) = 79.91. Hmmm. 

If Tp = Ta, there will be no convection loss, right? And if the
ambient air is not 100% humid, there will be evaporation heat loss.  
 
Does this equation apply when the air is warmer than the water, ie Ta > Tp?
There's an old reference: Bowen, I. S. Physical Review, 27B, 779 (1926)
"The Ratio of Heat Loss by Conduction and by Evaporation from Any
Water Surface." The title does not mention condensation, or talk about
heat gain at all, or suggest water can lose heat by evaporation and
gain by convection at the same time, but hey, why not?

>What else? Clausius-Clapeyron: ln Vp = 17.863-9621/(T+460),

Baruch Givoni has measured roofs that are 10 C cooler than surrounding air,
on clear nights. If the wind blows, it warms up the roof. Seems like this
would happen on a clear day, too, as another form of heat loss.
Why is the sky blue? Why are "solar pool covers" blue? 

>that falls on the cover... some of that eventually ends up in the pool...
>So we might take the pool cover off when the sun is shining if we believed
>that the increased gain (30 Btu/hr-ft^2, ie 10% of the peak solar input?)
>would be more than the 1 Btu/hr-ft^2-F increased loss by R1 conduction and 
>evaporation (which might be much more than that.) 

A perfectly transparent pool cover would not "shade the pool," nor would
a perfectly conductive one, I guess. "Solar pool covers" are close to both.

>in July?), and how much sun, and clouds and wind? 
 
Humidity ratio (W) is the ratio of water weight/dry air weight. Perhaps
NREL characterizes humidity by monthly average humidity ratios for various
places in their _Solar Radiation Data Manual for Buildings_ since W depends
less on air temperature than relative humidity (RH). Perhaps this says
there's a certain amount of water in the atmosphere, in a particular city,
and if the air temp goes up, RH goes down, and vice-versa, unless
condensation or evaporation occur, eg to or from swimming pools.

>>	Its sunny, warm and no wind	-off
 
If the air is warmer than the pool, and the air is moving, the pool gains
heat by convection, and loses heat by evaporation, right? If the air is warm
enough and humid enough, the pool gains heat by condensation, right? How warm,
and how humid? Would we ever want the pool warmer when that happens? Maybe.

>>>cover off at other times?
 
Sure. I wonder what that relationship is. 

Nick

  The main point is I want you to have fun in doing what you are trying to
  do for yourself or India or whatever. There is in fact no agenda that is
  or has to be laid out by me, and you follow it. You are self motivated by
  your fun and curiosity. Let me tell you a story.

  When I joined TIFR, we worked (or played) in a place called Holiday Camp.
  We were entitled to 90 days vacation in an year. So we were called 
  vacation officers in Holiday camp. We were not assigned any jobs. No
  agenda. We used to frequent the coffee tables, then magazine sections,
  then lunch, gossip, then coffee, and by 3pm, it was time to go. After six
  months of such fun, the fun became boring. We started wondering: why the
  heck we were being paid at all? From then on the story was entirely
  different. Work became play and play became work.

  Please note: it is not my project you are doing. It is your project,
  whatever that you are doing for the fun of doing it. You do not have to
  prove or disprove my ideas. You generate your own and be self referred.
  This is what I would like to see happen.
						Sastry

  Guruji feels that it will be imporant to teach organisational skills,
  team spirit and bonding, since the schools are teaching other standard
  educational aspects such as reading, writing and arithmetic. We all hear
  of how we Indians don't do well in groups, right? There is the well-known
  story of the Indian crabs. Also, someone was saying a few days ago that
  "one Indian equals three Japanese, but three Indians equal one Japanese".
  Not that we want to compete and beat the others, but the Japanese do seem
  to offer a valuable lesson to us here, in making the group (Japan Inc)
  an important entity. Guruji has been very impressed by the Japanese school
  next door, where the kids spend a few hours everyday in the sun, doing
  various group exercises such as forming patterns, then reorganising 
  themsleves etc. (the kind we see in parades). Guruji feels it will be
  good for us work on fun themes that involve group work and hence teach
  the value of this. 

  Some ideas we were discussing here were: have a set of circles each of
  some given colour, organised in some initial pattern (say a set of
  parallel lines). Then "morph" this into some other pattern, by moving the
  circles appropriately. This is a symbolic representation of the Japanese
  children's daily exercise. Each group (or child) is  assigned a certain
  colour, and by moving their circles appropriately, they see how a pattern
  froms by their individual moves. Or maybe, they are given building blocks
  to build a house--one child puts them together, another paints, another
  takes care of the environment around the house etc. Maybe we can start off
  creating group puzzles and activities like this that are fun for the kids,
  then maybe make them software packages that the children work with. 

  I think this can also help us enhance our group activity: I think many of
  us really dream of contributing to the work of SVT (or other such groups)
  and have largely similar goals, but we do seem to become unorganised and
  unfocussed at times, right? Maybe projects such as this will help us split
  the work appropriately through the Internet, and jointly brainstorm etc.

                                                   Aravind

  Thanks Aravind, this message itself tries to incorporate the group spirit
  we are talking about. Together, we can fly much higher than any one of us
  individually can (as long as we sit in each other's laps :-) Have fun!

						   Sastry

---

From: [email-masked] (Nick Pine)
Date: 8 Oct 1996 10:11:28 -0400

Andrew McKegney <[email-masked]> wrote:

>What Mr. Pine doesn't (want to) appreciate is that (existing) solar
>blankets -as simple as they are- are a bother to use, even with a roller,

Au contraire, I appreciate that... 

>and that most pool owner really don't want to look at them.

Perhaps that would change if they looked like a slate patio.

>They like the look of the water swirling and sparkling in the sun.

I enjoy watching house fires, sometimes. 

>A very important point about blankets has not be mentioned by others.
>That is the blankets don't work worth beans if they are wet!

We already talked about that, as regards R-value. Wet insulation has little.
Even 2% moisture in fiberglass insulation reduces its R-value by half, and
it's not hard to accumulate that much moisture in a house wall, if the vapour
barrier is not perfect. Wind is a problem with fiberglass too. Foam is better
this way, but R-value tests first developed and standardized by fiberglass 
insulation manufacturers use perfectly still, dry air for testing both, so
we don't hear much about the advantages of foam over fiberglass, in the
presence of water vapour and wind.  

>As I stated earlier blankets work by reducing evapouration. If there
>is water on top of them, that water evapourates,and pulls heat from
>the pool right through the blanket. It's like having holes in the blanket.

Good thought. Can we store heat in our slate pool cover patio all day,
and then submerge it briefly for a dip in the pool at dusk, to cool off?

Here's another recipe: make 1 picture-frame mold out of 2x4s on edge with
a 4'x8' id, and put a $16 4x8x2" Styrofoam panel inside and place 1.5" of
concrete on top of it, and push a 1/2" diameter hole diagonally through each
corner of the concrete, so you can tie these slabs together later. Repeat
26 times. Make the perimeter slabs with cedar strips and plated screws to
hold down a single $40 24'x36' sheet of 6 mil poly film, on top of the cover,
and inflate the film slightly to raise the cover and make a 768 ft^2 solar
collector, and lower it 2" every so often, letting some water leak in around
the lower film edges, using a thermostat, automatically, to remove the solar
heat. You can't walk on this, but it would keep the pool warm in December. 

Or build some air pockets under the cement slabs with some PVC drainage pipe
($3.88 for 4" pipe 10' long, at Home Depot), drilling a hole in the bottom
of the pipe to push air out of the pipe through a small piece of air tubing
stuck in the pipe, if you want to walk on water. Join the air pipes end
to end to attach the slabs? Use some imagination.

>During periods of bad weather the average pool owner doesn't swim, and
>unfortunately they don't watch the chemicals in their pool. If the pool
>is covered with a blanket it will actually stay reasonably warm...

Suppose our pool starts out at 80 F, and only loses heat through its 24 x 36'
R1 "solar pool cover" over a cloudy week in October, in Philadelphia, with
an average air temperature of 56.4 F. R = 1/768 and C is about 24x36x6x64
= 332K pounds of water, 166 tonnes. So RC = 332K/768 = 432 hours, 18 days.
Nice :-) So T = 56.4 + (80-56.4) exp(-t/18), where t is in days, 78.7 F
after 1 day, 77.5 after 2, and 72.4 after 7 days.

With an R10 pool cover, we'd have an RC time constant of 180 days, so
T = 56.4 + (80-56.4) exp(-t/180), where t is in days, 79.9 after 1 day,
79.8 after 2, and 79.1 after 7 days with the cover on. Hmmm.

In December, we might have T = 35.8 + (80-35.8) exp(-t/180), 79.8 after 1 day,
79.5 after 2, and 78.3 after 7 days with an R10 cover on. Or T = 35.8 +
(80-35.8) exp(-t/18), 77.6 after 1 day, 75.4 after 2, and 65.8 after 7 days
under an R1 cover. Not too bad, but too cold for swimming.

During a long string of average December days, with some sun, a square foot
of this pool with the perfectly insulated side walls and R1 "solar pool cover"
would absorb about 500 Btu/ft^2/day of sun and lose 24(T-35.8)/R1, so
T = 35.8 + 500/24 = 56.6 F. Not warm enough. Adding an overhead reflector like
a 15' tall commercial plastic film greenhouse with the north poly film painted
white or ferrocement over an interesting half-dome armature made of 2x4s and
chicken wire might add 800 Btu/ft^2/day so T = 35.8 + 1300/24 = 90 F. Hey.  

But with uninsulated sidewalls, we need a better pool cover, Andy, eg an
automatically-movable one that collects sun during the day and really
holds it in at night... 

>NEVER, NEVER swim on or over a plastic film pool cover. Many people have
>drowned from trying this. Mr. Pine has made a very dangerous and foolish
>suggestion in an earlier post about having a plastic cover sink to the
>bottom of the pool.

I have NEVER, NEVER suggested swimming under a pool cover
when it is on the bottom of the pool.

Especially a slate one. Unless one is a Mafia leader in disfavour...

("Guido decided to investigate the pool cover, from underneath.")

Nick

---

From: [email-masked] (Nick Pine)
Date: 8 Oct 1996 07:59:08 -0400

Andrew McKegney <[email-masked]> estimates:
 
>Yes you should use the pool cover at night if you want the pool to
>stay the same temperature. If your pool is warmer than the air temp,
>it will lose very little heat overnight, conversely...

Let's see: on a single October night, where I live, with an average air
temp of 46.4 F, an 80 F pool with 24' x 36' R1 cover would lose about  
16 hours (80-46.4)24x36/R1 = 464,486.4 Btu, the heat equivalent of about
4 gallons of oil. How many 8 oz. cups of tea could we make with that heat,
starting with 62 F water? Heating each half-pound of water to 212 F takes
1/2(212-62) = 75 Btu, so we could make 464,486/75 = 6,193 cups of tea.

A kitchen match contains about 1 Btu, so we could also do this by standing
under the pool and burning 464,486 matches per day, ie 19,353 matches per
hour or 322 matches per minute or 5 matches per second, for 24 hours a day.

Hey, renewable energy! :-)

Nick

---

From: [email-masked] (Nick Pine)
Date: 8 Oct 1996 08:15:10 -0400

>Ta - 3(80-Ta)exp(17.863-9621/(Ta+460)) = 79.91. Hmmm. 
 
Aha, shoulda writ:

How close would the air temp have to be to the pool temp, to make it worth
taking the "solar pool cover" off? Looks like the breakeven point is when 
30 = (80-Ta)(1+1000(1.079-0.333)) = 747 (80-Ta) = 59760 - 747 Ta, so 
Ta = (59760-30)/747 = 79.96 F. So it might make sense to remove the cover
to let more sun shine into the pool, if the air is no more than 0.04 F
cooler than the pool, and there is no wind, in Philadelphia in October.

Probably not worth the trouble, eh?

Nick

---

From: [email-masked] (Nick Pine)
Date: 8 Oct 1996 11:08:20 -0400

>heat. You can't walk on this, but it would keep the pool warm in December. 

Come to think of it, you could walk on it, if the poly film cover were
sufficiently inflated. Poly film pillows on commercial greenhouses are up
to 3' thick, as inflated on 4' centers, and they hold up more than 15 psf
of snow, so a pool cover like this could be 36' tall in the middle, with a
3' rise every 2' in from the edge. We might paint the north side dark, or
hang some greenhouse shadecloth across the middle, and blow down some air
>from  the top through floatation pipes in thermal contact with the water,
to collect more solar heat. I'd clip this cover to the edge of the pool
for parties, so we don't somehow end up like Guido.

There must be a simple way to make an airtight door in the film itself...
Overlap 2 pieces of film, and slip between them to get in?   Not quite...

Nick

---

From: [email-masked] (John Harrison)
Date: Tue, 08 Oct 1996 20:24:40 GMT

Well thanks guys!
I'd hate to see the long and complicated answers!!!!
Nick's technospeak had me a bit baffled and the earlier response
"seems" to make some common sense to me.
I got the impression that Nick thinks that the cover should be on at
all times to prevent evaporation rather than have any exposure to
warmer air temps - is this correct. 
At all air temps??? It gets to 90F regularly in summer here but we
still like warmer water!

---

From: [email-masked] (Nick Pine)
Date: 8 Oct 1996 22:39:59 -0400

>warmer air temps - is this correct. 

This seems like the simplest strategy.  

>At all air temps??? It gets to 90F regularly in summer here but we

If the air is humid and warm enough to warrant removing the pool cover, you 
might not want the pool warmer. You might answer this question more exactly
with a simulation, using real local weather data, or build a couple of
minipools side by side, one with and one without a cover, and control the
big pool based on the minipool performance (?) As Andy said, this is not 
a simple question, but it may well be an unimportant and insignificant one.

Nick

---

From: [email-masked] (Andrew McKegney)
Date: Tue, 08 Oct 1996 20:19:57 GMT

>Perhaps that would change if they looked like a slate patio.

Perhaps, but they would not like trying to remove them !!

>I enjoy watching house fires, sometimes. 

Say, do you like watching burning churchs too? Perhaps I should pass
your name on to authorities in Georgia.

>We already talked about that, as regards R-value.
I'm not talking R value, as solar blankets have virtually none.

Note: the following is useless information for pool owners.

 Wet insulation has little.
>presence of water vapour and wind.  

Note ends.

>heat. You can't walk on this, but it would keep the pool warm in December. 

It "might" (highly unlikely) keep your pool warm, but I don't know of
many people who ae going to want to shovel the snow off the cover
before they sink it (along with the dust dirt, leaves, dead bugs,
etc.) before they go for a swim.

>after 1 day, 77.5 after 2, and 72.4 after 7 days.

Most pool owners would be very happy that their pool only lost 1-2
degrees per day with the outside temperature being only 56. As I have
pointed out, a conventional solar system will easily reheat the pool
2-4 degrees on a sunny day. (for free)

With your imaginary R10 blanket that magically appears and dissappears
>from  the pool surface without any effort by the pool owner, things
could be even better. But then this is pure fantasy.

>when it is on the bottom of the pool.

No, you have suggested swimming over the top of a submerged plastic
pool cover. Just as bad and dangerous!!!!! This is a totally stupid
idea and I hope anyone who loses a family member because of your
suggestion, sues your ass off !!!!

You are way over your head when it comes to talking about heating real
pools with solar systems. I suggest you quit before you drown.

Andrew McKegney

---

From: [email-masked] (Andrew McKegney)
Date: Tue, 08 Oct 1996 20:31:39 GMT

>Hey, renewable energy! :-)

A typical volume of water for a pool of those (uncommon) dimensions
would be: 24 x 36 x 5 (average depth) =4320 ft^3
Weight = 4320 x 64.2 =277344 lbs
therefore drop in pool temp = 464486btu/277344btu/degree = 1.67
degrees.

A pool owner is going to be very happy that his pool only cooled by
that much. A properly sized and installed solar system will also add
about 600,000 btu's to the pool raising the temp by 2.25 degrees.
Passive solar gain through the blanket would add to this, probably by
2 more degrees.

Andrew McKegney

---

From: [email-masked] (Guy Macon)
Date: 9 Oct 1996 11:56:01 GMT

>At all air temps??? It gets to 90F regularly in summer here but we

I heard that in Pheonix, AZ, the set up fountains to stop
pools from getting too hot to swim in...

---

From: [email-masked] (Nick Pine)
Date: 9 Oct 1996 16:34:34 -0400

Andrew McKegney <[email-masked]> wrote:
 
>>>...most pool owner really don't want to look at them.

The eyes want to look but the body does not? 

>Perhaps, but they would not like trying to remove them !!

Perhaps you have not had time to read the 10 lines you quoted below.

>before they sink it

Those pool owners might prefer the inflatable version, described in the
10 lines you quoted above (note the plastic film should terminate below
the water line, to make a dry floor and a good air trap) with the oblong
poly film dome 12' high in the middle, and the inside of the north half
of the plastic film painted white to reflect more sun down into the water
on top of the cover, during the day.

Should we inflate the cover with Grainger's $60 1" 140 cfm 100 watt blower,
the one used to inflate greenhouse poly film pillows? Or the leaf blower
that Sears Hardware is now selling for $49.95 (8.5 A 110V, 340 cfm at 150 mph)
We might make a pressure switch with a manometer and a floating magnet and
reed switch. Or find a 13 year old science fair student or a serious solar
pool heating professional to solve this pressure control problem. Another
cordless 12 VDC (allowing easy backup power) 16 A version blows 70 cfm at
110 mph, which might raise a 24' x 36' slate pool cover from the bottom in
2 minutes, or turn on for a few seconds every 4 hours to keep it afloat.

Their $69.95 wet/dry shop vac might make a good bubble generator, with the
vacuum hose connected to the top of the cover and a bubble sensor to turn
the vac on when there are no bubbles at the top.

Use some imagination, Andy.
 
>could be even better. But then this is pure fantasy.

Like telephones or moonwalking or wireless electronic doorbells or plastic
film greenhouses? Perhaps you imagine skyscrapers and airplanes are built
by trial and error :-) Some things are fairly predictable. Like you.

Nick

Wise men learn more from fools
Than fools learn from wise men.  --fortune cookie

---

From: [email-masked] (Andrew McKegney)
Date: Wed, 09 Oct 1996 20:16:52 GMT

>pools from getting too hot to swim in...

96:10:09

Yup that works because of evapourative cooling, but you  can lose a
lot of water that way.

Another approach that solar pool heater owners can use is to run the
solar systems at night. (In fact some of the better solar controllers
have an "over temp" feature built into them which will cause the water
to flow through the panels at night if the pool gets too warm - a
feature we really don't need here in Canada!)

The solar panels lose heat to the sky (which has a cooler temperature
on clear nights than the air), which cools the pool down. As noted
this only works well if there are no clouds.

Andrew McKegney

---

From: [email-masked] (Andrew McKegney)
Date: Thu, 10 Oct 1996 05:39:52 GMT

[email-masked] (Nick Pine) continued to spew:

>>many people who are going to want to shovel the snow off the cover
>>before they sink it

>>could be even better. But then this is pure fantasy.

If you think this idea is so hot why don't you build one. I'd wager
dollars to donuts that you could not make a practical product that
could be sold to compete with the products currently on the market.

BTW the latest issue of Pool & Spa Marketing has a feature on pool
covers and rollers. You might actually learn something about pool
covers if you were to read it.

Available from:	 Hubbard Marketing and Publishing
		270 Esna Park Drive, Unit 12
		Markham, Ontario, Canada. L3R 1H3
		905-513-0090

You should get a copy - you have a lot to learn about pools.

Andrew McKegney C.E.T.

---

From: [email-masked] (Seamus)
Date: Thu, 10 Oct 1996 17:06:58 GMT

>You should get a copy - you have a lot to learn about pools.

I for one have just about had it with this arrogant salesperson and he
gets my killfile vote.

The day is better already.
Jim

---

From: [email-masked] (Nick Pine)
Date: 10 Oct 1996 13:28:17 -0400

>could be sold to compete with the products currently on the market.

I'll pass on that. Seems to me solar ovens and pools are luxuries in this
country, as long as we are heating our houses with oil and bombing Iraq
to keep the price low. This keeps Canadian oil prices low too, I guess.
 
>		 Markham, Ontario, Canada. L3R 1H3

Thanks for the tip. I called 'em, and they are sending me a free copy :-)

Nick

Nicholson L. Pine                      System design and consulting
Pine Associates, Ltd.                                (610) 489-0545 
821 Collegeville Road                           Fax: (610) 489-7057
Collegeville, PA 19426                     Email: [email-masked]

Computer simulation and modeling. High performance, low cost, solar heating and
cogeneration system design. BSEE, MSEE. Senior Member, IEEE. Registered US
Patent Agent. Solar closet paper: http://leia.ursinus.edu/~physics/solar.html

From [email-masked] [email-masked] Wed Oct 16 22:38:22 EDT 1996
Article: 1264 of alt.solar.thermal
Path: newz.oit.unc.edu!concert!gatech!csulb.edu!news.sgi.com!howland.erols.net!newsfeed.internetmci.com!uunet!in3.uu.net!ausnews.austin.ibm.com!brandonm
From: [email-masked] (Brandon Mayfield)
Newsgroups: alt.solar.thermal,alt.energy.renewable,sci.engr.heat-vent-ac
Subject: Hey, Nick!
Date: 10 Oct 1996 18:49:56 GMT
Organization: varies with the inverse of the frustration
Lines: 23
Distribution: world
Message-ID: <[email-masked]>
References: <[email-masked]> <[email-masked]> <[email-masked]>
Reply-To: [email-masked] [email-masked]
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Originator: [email-masked]
Xref: newz.oit.unc.edu alt.solar.thermal:1264 alt.energy.renewable:18522 sci.engr.heat-vent-ac:9433

In article <[email-masked]>, [email-masked] (Nick Pine) writes:
> barrier is not perfect. 

 2% moisture by weight, volume, or what?

 I'm insulating a house in the next couple of weeks - could I use 
 something besides fiberglass to avoid this problem? How about some
 kind of foam, or polystyrene (sp?). Got any recomendations of brands
 etc.? What's going to get the biggest bang for the buck?

 I'm stuck with the 2x4 exterior walls covered with Tyvek house wrap / 
 masonite siding. I was not especially worried about a vapor barrier 
 (just using kraft backed 'glass bats) since there's no vapor barrier 
 on the outside wall and the %RH is typically just slightly lower than, 
 say, Houston (I'm in Austin, Tx.).

 Brandon Mayfield

---

From: [email-masked] (Nick Pine)
Date: 10 Oct 1996 18:14:14 -0400

Brandon Mayfield <[email-masked] [email-masked]> wrote:
>[email-masked] (Nick Pine) writes:
>> 
>>it's not hard to accumulate that much moisture in a house wall, if the vapor
>>barrier is not perfect. 
>

I don't recall. Heard this from David South at last year's Monolithic Dome
conference. I think he said 6% was typical, if the vapor barrier is poor. 
That would be 4 pounds of water per cubic foot of fiberglass by volume :-)
Perhaps it's by weight.

> etc.? What's going to get the biggest bang for the buck?

Fiberglass is the bigger bang. Cheaper than straw, at 25 cents/R20-ft^2,
ie 1.25 cents/R-foot, like board-foot. Cheaper than straw in some stores, at
$4/R50-4 ft^2 strawbale, ie 2 cents/R-foot. Not as cheap as a bubblewall, tho.
 
> say, Houston (I'm in Austin, Tx.).
 
Do y'all put the vapor barrier on the inside or outside of the insulation
down there? Perhaps you should consult with your local HVAC criminal.

("Guido? Nah, Guido's not around anymore. He had a unforchunate axident.")

Nick

---

From: [email-masked] (Sylvan Butler)
Date: 11 Oct 1996 03:30:21 GMT

>solar systems at night. (In fact some of the better solar controllers
 ...
>on clear nights than the air), which cools the pool down. As noted

This makes absolutely no sense.  The amount of radient energy in 100deg
water is trivial.  Isn't the air temp the only concern, and the air temp
is usually cooler on clear nights?

sdb

---

From: [email-masked] (Andrew McKegney)
Date: Thu, 10 Oct 1996 18:14:58 GMT

>Nick

Nick inflatable pool covers are not new, they have been around for
years and they are not cheap. (Check out the latest issue of Pool and
Spa Marketing) Plus in winter months you have to heat the air you use
to inflate the cover, or it's like standing naked in a blizzard !

You have to use a blanket on the pool or the convective heat losses
are incredible. Nothing like ice-cold condensation to chill-out a
swim. (I know, I been there, done that).

Again you're way out on the end of a 100 metre diving board, and all
you know is the theory of diving - hell it can't be that hard to fall
down! Recant --- before you do a(nother) belly-flop and splatter your
ignorance over the web.

Andrew McKegney C.E.T.

---

From: [email-masked] (Andrew McKegney)
Date: Fri, 11 Oct 1996 01:11:49 GMT

>The day is better already.

It would appear Jim that  you  don't know what your talking about
either, Just like your friend Mr. Pine

Andrew McKegney C.E.T.

---

From: [email-masked] (Nick Pine)
Date: 11 Oct 1996 06:44:02 -0400

Sylvan Butler <[email-masked]> wrote:
  ...
>is usually cooler on clear nights?

100 F water has a an absolute temp of 560 R, no? It radiates energy at about
0.174 x 10^-8 560^4 = 171 Btu/hr-ft^2 to the surroundings, which also radiate
energy back at the water. If the surroundings have a temperature of 0 F,
they only radiate heat back to the water at a rate of 78 Btu/hr-ft^2, for a
net heat loss of 93 Btu/hr-ft^2. Perhaps a clear sky can be colder than 0 F. 
 
Nick

It's a snap to save energy in this country. As soon as more people become
involved in the basic math of heat transfer and get a gut-level, as well as
intellectual, grasp on how a house works, solution after solution will appear.

					  Tom Smith

---

From: [email-masked] (Nick Pine)
Date: 11 Oct 1996 10:58:52 -0400

Nick Pine <[email-masked]> wrote:

>Perhaps these are opaque baby-blue aesthetically-interesting inflatable effete
>and pool covers, vs serious virile poly pool covers that stand tall...
  ^
Oops. A typo. I thought I'd deleted all of "and faggoty pool covers," so as
not to offend my faggoty friends, by implying they were solar pool heating
professionals, or worse. (What could be worse?) Sorry... 

Nick

---

From: [email-masked] (Nick Pine)
Date: 11 Oct 1996 10:51:51 -0400

Andrew McKegney <[email-masked]> oozed:
 
>years and they are not cheap.

Commercial plastic film greenhouses have been around since the 60s,
and they cost 57 cents per square foot. Inexpensive erections, too.
Perhaps solar pool heating professionals are accustomed to paying
large sums for erections.

>(Check out the latest issue of Pool and Spa Marketing)

There are many ways to do things wrong, as Edison found out
9,999 times with light bulb filaments.

>Plus in winter months you have to heat the air you use

Perhaps these are opaque baby-blue aesthetically-interesting inflatable effete
and pool covers, vs serious virile translucent poly pool covers that stand tall
and proud, with their feet in the pool water itself, and their north halves
painted white to keep the sun from shining in one side and out the other, as
they bounce it down into the pool water washing over their solid slate patio
decks. Perhaps their lower plastic film edges are not underwater, holding up
a slate pool patio, so they don't leak very much air, like a well-sealed
1 acre greenhouse poly film cover inflated with a single 50 watt blower.
 
>are incredible.

We already covered that. 

>down! Recant --- before you do a(nother) belly-flop and splatter your

Nonono. I won't recant. I splatter my ignorance in your general direction.
Here's the plan du jour:

Article 2375 of alt.architecture.alternative:
From: [email-masked] (Nick Pine)
Subject: Re: Solar Pool Heating
Date: 10 Oct 1996 11:57:45 -0400 [updated 10/11/96]
Organization: Villanova University

Why not add a plastic film greenhouse onto the south side of your house, or
build yourself a plastic film greenhouse in the sun near your house, within
20' say, with a couple of underground pipes for warmwater heat transfer from
a strawbale tank lined with EPDM rubber for space and water heating?

If the greenhouse were very near the house, say within 10', some of the
solar "waste heat" from heating the water tank could heat the house with
warm air. A greenhouse might be a fine place to put your central air outdoor
unit, if it can work as a heat pump in the winter. 

Stuppy (800) 877-5025 sells 20' wide x 10' tall greenhouses for 64 cents
per square foot, up to 48' long, 57 cents if longer, plus about $200 for
shipping from Kansas City, and a 30' wide x 100' long x 15' tall 3,000 ft^2 
greenhouse can be put up by 3 people in one day, from scratch, including
the ground stake "foundation." The standard way to keep the plastic film
>from  fatiguing in the wind in the winter is to use two layers and inflate
it to 1/4" water column pressure with a $50, 50 watt blower. You might only
turn on the blower when it is windy, or just use 1 layer of plastic and some
sort of ridge venturi to make a slight vacuum inside when the wind blows.

As an alternative to those standard quonset hut or gothic arch-shaped
greenhouses made with curved galvanized pipes, you might spend another
day making the 18 curved beams you'd need for a 16' wide 8' tall x 32'
long greenhouse out of 36 12' 1x3s costing $2 each, bending two of each
to an 8' radius, with some 1x3 spacers and purlins and ridgepole every 2',
held together with deck screws, for a $200 512 ft^2 structure to collect
and store about 200K Btu of sun per day, about 2 gallons of oil's worth,
on an average December day.

These 1x3 beams fail in horizontal shear, slipping when you put the ends on
the ground and push on the curved top side. So they could use some glue, and
a solid middle 1x3, or a little chicken wire on each side of the 1x3 spacer:

     -----------------------------------------------------------

                            12' 1x3

     -----------------------------------------------------------
                     |    chicken wire   |
                     |   1x3x3x3 spacer  |
                     |     every 2-3'    |
                     |    chicken wire   |
     -----------------------------------------------------------

                            12' 1x3

     -----------------------------------------------------------

It might look something like this:

     ---                  .
                   .      c      .            The 10' x 32' R10 insulating 
               .               c     .        and reflective cover is shown  
      8'     .                      c  .      in the raised position.
           .                            c.
          . plants,       b "solar" pool  b   ---
         .  picnic table, a    cover      a.
        .   etc.          l  106 F water? l .  4'
     .....................e...............e..................
        |                16'                |

                          |       11'       |
        .....................................
        .                 . . . . . . . . . . ---
        .                 . .      8'     . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . . 30'         . . 32'
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . . . . . . . . . .
        ..................................... ---

The tank might be 8' wide x 4' deep inside, made with about 80 strawbales
and a few 2x4s and dacron rope and ground stakes, and a single piece of EPDM
rubber, 20' wide x 44' long. This piece of rubber might drape over the top
of moldy old $1 strawbales, with the sides uncovered, all natural-like, with
a plastic film vapor barrier underneath. (Yuppies and architects might use 
bright yellow $2 strawbales, with accent pumpkins.)

The cover might be

1. rigid as shown, weighing 300 pounds at 1 lb/ft^2?, made with $160's worth
of 4x8'x2" Styrofoam sheets and a few 2x4s, painted white underneath and dark
on top, with a counterweight, small reversible motor and photocontrol, or

2. a $24 flat polyethylene pillow, filled with tiny cold bubbles at night, and
air during the day, using a $50 wet/dry shop vac with a bubble sensor in the
return line (how do we make that?) to make bubbles out of a soapy water puddle
at the bottom of the plastic film and collect them at the top, for a few
seconds every few hours. The cover might be on the bottom if people were in
this large hot tub, and they would want to be careful to neither slip nor
puncture the plastic film, nor crawl underneath, as one solar pool heating
professional suggested. The north half of the poly film overhead might be
painted white, to reflect more sun down into the water on a winter day.

3. Another way to make a cover is to assemble $30 worth of 4" solid thinwall
PVC drainage pipe on the floor of the tank, into a 30x8' picture frame, lay
some plastic mesh on top for reinforcement, place an inch of concrete over
that, then $120 worth of 2" Styrofoam on top of that, and some very thin
thin reinforced concrete slabs, pieces of slate, or 1/2" of pebbles over that.
If all goes well, when you fill the PVC pipe with a little air at 2 psi from
a 340 cfm, 150 mph $49 Sears leaf blower (?) to make a maximum bouyant force
of about 640 pounds, the cover might magically rise up to the top, and people
could sleep on it at night. A guest room. With a klaxon and automated
"Dive! Dive! Dive!" announcement a few seconds before the cover sinks at dawn
the next morning to absorb sun into the water through a single layer of
plastic film on top?

4. Or, you might lift the neutrally-bouyant slab with a polyethylene film
cover on top, by inflating that. More at night than during the day, when
the floor would be awash. Or you could haul the cover up out of the water
with a rope harness and a $149 Sears garage door opener, which some people
use to haul boats out of the water.

This could become a serious hobby. Or even a business.

What would the average water temperature be in December? Where I live,
the south wall might receive about 1000 Btu/ft^2/day of sun, of which 90%
might make it through the outer layer of plastic film and 80% be reflected
>from  the white surface overhead, and 90% of that might fall into the water,
so the average daily solar gain into the water might be 1000x256x0.9x0.8x0.9
= 166 K Btu. The greenhouse might be 70 F on an average December day in the
Philadelphia area, with some sun, or warmer if there's a reflecting surface
to the south. 

The pool would mainly lose heat through the "solar pool cover," over a 6 hour
solar collection day, so if there were no useful heat output from the pool,
it might have an average steady-state stagnation water temp T such that
166K Btu = 6(T-70)240 ft^2/R1 ==> T = 70 + 166K/(6x240) = 185 F. Warm enough
to cook lobsters?

The thermal conductance of the pool with the cover in place would be about

    320 ft^2/R10 = 32 for the cover,
  + 320 ft^2/R50 =  6 for the walls,
  + 320 ft^2/R10 = 32 for the bottom,
    for a total of 70 Btu/hr-F,

and the average temp inside the greenhouse might be 50 F in December, so if
the pool temp were 130 F, say, the top and sides of the pool might lose
24(130-50)70 = 134 K Btu/day, and the 4x8x32x64 = 65,536 pounds of water
might lose 134K/66K = 2 F on a cloudy day, and another 2 F if it supplied
a modern house with the heat equivalent of a gallon of oil per day.

And another 1 F if it were supplying hot water for the house, via some hot
water plastic pipe running around the top edge... How much plastic pipe area
do we need to heat 3 gpm of water from 55 F to 110 F in 130 F water? We need
to transfer 3x8x(110-55) = 1320 Btu of heat in a minute, or about 80 K Btu/hr
(23 kW), which we might do across a liquid-liquid interface with an R0.1 thin
PVC pipe wall between (copper pipe might make this R0.03, and tend to inhibit
algae growth in the pool), with an average temperature difference of something
like 50 F, so we'd need a pipe surface area A such that 80K = 50 A /R0.1, so 
A = 0.1x80K/50 = 160 ft^2. A $4 10'x4" PVC pipe has an area of Pix4/12x10
= 10.5 ft^2 and a volume of 3.14x(1/6)^2x10 = 0.87 ft^3 (which would displace
$1.77 worth of concrete at $55/yd^3.) So, do we need 16 of these 10' pipes?
I don't think so, since we do not or should not use 3 gpm of hot water for
more than about 20 minutes at a time, ie 60 gallons or 7.5 cubic feet, or
about 8 pipefuls of water, or 80 linear feet of pipe, once around the top
edge, just under the water surface. 

Now, how can we keep this pipe half full of air, to float the pool cover?

Nick

Computer simulation and modeling. High-performance, low-cost solar heating and
cogeneration system design. BSEE, MSEE. Senior Member, IEEE. Registered US
Patent Agent. Solar closet paper: http://leia.ursinus.edu/~physics/solar.html

---

From: Will Stewart <[email-masked]>
Date: Fri, 11 Oct 1996 21:53:44 -0400

> is usually cooler on clear nights?

Radiant energy is exchanged with the night sky, which can be "seen" by
the panels at very low temperatures.  Any number of factors, i.e.,
cloudy cover, smog,etc can reduce the transfer rate.

An intro to thermodynamics would be a good investment.

-- 
William R. Stewart
http://www.patriot.net/users/wstewart/first.htm
Member American Solar Energy Society
Member Electrical Vehicle Association of America
"The truth will set you free:  - J.C.

"Troll:
     A deliberately disrupting, confused and incorrect
     post (or one posting trolls) to a Usenet group to
     generate a flurry of responses from people called 
     "billygoats" trying to set the record straight.
     Other trollers enter the fray adding more and more
     misinformation so that the thread eventually dies of
     strangulation.  Trolls/trollers cannot be affected
     by facts or logic."    - [email-masked]

---

From: [email-masked] (Andrew McKegney)
Date: Fri, 11 Oct 1996 21:14:30 GMT

Andrew McKegney C.E.T.

---

From: [email-masked] (Andrew McKegney)
Date: Fri, 11 Oct 1996 21:13:52 GMT

>net heat loss of 93 Btu/hr-ft^2. Perhaps a clear sky can be colder than 0 F. 

I believe your calculations are resaonably accurate (after having
checked my ASHREA handbooks), but you didn't follow through to
illustrate the significance of the heat loss.

If we use the surface area of the  pool you have previously used (24'
x 36') we end up with a heat loss of 93 x 864 = 80352 BTU / hr. Using
a 10 hour "night" that becomes 803,520 BTUs. 

If the pool has a volume of water 270,000 lbs of water, this heat loss
would be equivalent to 803,520/270,000 = 2.98 say 3.0 degrees F.

That is only the heat loss by Radiation. Heat losses from
convection/evapouration and conduction (to the ground) are in addition
to this.

If the pool is covered, all forms of heat loss will be significantly
reduced. The solar panels will lose heat primarily by radiation to the
night sky, if the air temperature is the same as the pool temperature.
If water is sprayed onto the solar panels at night they will also lose
heat by evapouration. (Not recommended in areas with hard water. Hard
water deposits would likely reduce the absorbtivity of the solar
panels.) This approach is far better than draining warm water from the
pool and adding cold water, as you take advantage of the latent heat
of cooling (requiring 144 times less water).

Andrew McKegney C.E.T.

---

From: [email-masked] (Nick Pine)
Date: 12 Oct 1996 09:02:01 -0400

Andrew McKegney <[email-masked]> wrote:

>...adding cold water, as you take advantage of the latent heat

Sounds like you are adding ice.

Nick

---

From: [email-masked] (Nick Pine)
Date: 12 Oct 1996 08:58:27 -0400

Which is less expensive or more convenient for space heating, more solar
glazing and thermal mass, or more insulation? And how little backup fuel do
we want to use? A direct gain house can easily save 20% of an oil bill, but
to save or 90 or 100%, we need to change techniques. Steve Baer says it's
easy to make a 100% solar heated house. Just turn off the backup system.
He also says the greatest discovery of solar investigators has been that
if we use lots and lots of insulation, we need very little heat for a house,
>from  the sun or any other source. But superinsulation doesn't heat water.

And when David Boyer and I put 200 free 55 gallon drums full of water in his
local $1000, 20x100' R1 plastic film greenhouse last winter, a structure the
size of a house, with 1/20 the usual wall insulation, his propane heating
bill changed from $8,000 the winter before to $1,500 last winter. That was
a better first step than insulation. And I only used 25 gallons of oil last
winter to heat my old 4 bedroom stone house with 2 R10 and 2 R2 walls. 

We might build a 100% solar house in the Seattle that has a very large time
constant, and no solar glazing at all. Open it up in the summer, and let the
air heat it up, and close it up more in the winter, when it's cold outside.
How about a Monolithic Dome, half full of water, with a houseboat inside? :-)

An indoor pool, perhaps with fish... A water supply and heat sink and sewage
treatment system? Monolithic has been building these domes for 20 years now,
all over the world, and some of them are very large, eg 260' hemispheres,
and they have been used as water tanks, with no extra waterproofing. So...
Hire someone to build the dome in the normal way, for $25/ft^2 of base area,
then build a house inside, without much weatherproofing, then seal up the
dome door below and flood it? No need to worry about floods :-)

Or hold up the house with beams or cables into the concrete walls, in a more
normal way, and excavate first, so the pool is underground, and the house is
at ground level... In that case, the foam and concrete might not need to be
so thick. How would we warm or cool the water? Perhaps let air flow in over
the water through some holes in the dome perimeter at ground level, with a
vapor barrier floating on top of the water. 

How big would the dome have to be to get through a 6,000 degree day F winter
with a temperature change of less than 10 F, without using any solar glazing
at all? We need a time constant of about 1 year, roughly 10,000 hours. A
standard Monolithic Dome hemisphere has 3" of R20 exterior foam with 2" of
reinforced concrete inside. Filling it up with water completely makes
RC = 20/(2Pir^2) x 2/3Pir^3x64 lb/ft^3 = 427 r = 10,000, so r = 10,000/427
= 24 feet. If the 300 tons of water inside were 78 F in the fall, and it
lost 24x6000x1152ft^2/R20 = 8 million Btu of heat over the winter, the water
would be 65 F in the spring. Expand the dome to 40', a more normal size for
a house, use less water, add some solar glazing, eg some windows above, or
a transparent skirt around the lower south quarter, outside of the foam, with
an air gap between, and a Northwest winter should be no problem.

How about building a house on top of a strawbale pond foundation, inside a
$1/ft^2 commercial plastic film greenhouse? The ponds might be 2 bales deep,
about 32" tall, inside a standard 30' wide greenhouse like this: 

     ---                  .
                   .             .           
               .                     .          
     15'     .                         .     
           .                             .
          .                               .   
         .                                 . ----
        .b                b                b. 32" 
     ....b................b................b.................
        |                30'                |

        .....................................
        . . . . . . . . . . . . . . . . . . . ---
        . .               . .     13'     . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . . 62'         . . 64'
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . .               . .             . .
        . . . . . . . . . . . . . . . . . . .
        ..................................... ---

The 2 ponds might be 13' wide x 62' long x 32" deep inside, made with about
170 bales and a few 2x4s and dacron rope and ground stakes, and 2 pieces of 
EPDM rubber, 20' wide x 70' long. They would each hold about 17K gallons of
water, enough for a good water supply. And enough to hold the structure
down without using any ground stakes, eg on a flat city roof.

The house might sit on a $3/ft^2 Corruform concrete slab, poured on top of
currugated metal, as in office construction, or some thin reinforced 15'x 8'
concrete slabs, with a rib along the bottom. The concrete would act as a
vapor barrier above, and we might add a vapor barrier under the concrete,
eg a floating vapor barrier on the water, some sort of plastic film or oil.

Build the house out of strawbales, too? Unweatherproofed ones, since this
house is out of the weather. With an arched unweatherproofed roof with bales
running lengthwise south to north, on top of a vapor barrier, with 2x4s on
18" centers running east and west under that, attached to some flat arched
2x4s under that, and a few horizontal north-south tension members under that?

As to thermal performance, strawbales are about R50, so we have (roughly)
RC = R50/2000 ft^2x32"/12x2x13x62x64 = 6877 hours, or 287 days or 41 weeks
or 9.4 months. Not quite passive annual heat storage, but this stucture has
a lot of glazing, and it could have a ceiling fan blowing some warm air down
under the length of the floor. If we start off with this house at 68 F on
December 1, where I live, where the average December temperature is 36 F,
it might cool to 36 + (68-36)exp(-30/287) = 64.8 F after a cloudy month.
We rarely get 30 cloudy days in a row. Perhaps that happens more often in
Seattle, where the average December temperature is 40.5 F, and the average 
amount of sun that falls on a south wall in December is 420 Btu/ft^2/day.

How warm could we make this house in Seattle? 420x15x64x0.9 = 363K of sun
might get into the greenhouse, on an average 6 hour solar collection day,
and if the strawbale roof touched the peak of the greenhouse, so not much
heat was lost from the north side during the day, 6hr(T-40.5)960ft^2/R0.8
= 7200(T-40.5) Btu/day would be lost through a single layer of poly film,
and another 18hr(T-40.5)2000ft^2/R50 = 720(T-40.5) Btu would be lost during
the night, so 7920(T-40.5) = 363K, ie T = 40.5 + 363K/7.9K = 86 F.

Sounds good to me, especially since we didn't count the sun that falls on a
horizontal surface in December. Or in June. But cooling is another story. 

Nick

---

From: Brian K Petroski <[email-masked]>
Date: Sat, 12 Oct 1996 18:06:45 -0500

> winter to heat my old 4 bedroom stone house with 2 R10 and 2 R2 walls. 

     I agree.  We can build 100% solar homes with sufficient thermal mass 
and only moderate insulation.  My plan is to build a 40' wooden geodesic 
dome and cover it with an earth mound.  Then a few inches of  insulation 
on th mound and another earth covering, enough to let grass root on top 
of it.  The house will have solar gain from the southern exposed face and 
summer heat will be pumped into the mound through air tubes.  In the 
winter the air flow will be reversed to take the heat out of the mound 
into the house.  This design in for Minnesota and I see no reason it 
won't work anywhere in the U.S. simply by adjusting the size of the mound 
and the times when the air flow runs.  In southern states for example a 
rather small mound can store daytime heat for cool nights and thereby 
also provide a level of air conditioning.

			    Brian Petroski
			Just your stereotypical
			      polysexual,
			       bisexual
			    solitary pagan
		       from St. Paul, Minnesota

---

From: [email-masked] (John Harrison)
Date: Sat, 12 Oct 1996 21:16:01 GMT

I am STILL not sure from all the hype and calculations when I should
take my cover off if the air temp is warmer than the water temp?????
Forget philadelphia!
This is Brisbane Australia!
During the day (like now at 6a.m ) it is around 18 C and will get up
to 26-28 C during the middle of the day and go bback to 15-16
overnight.
My pool temp is about 22C - late afternoon, and I haven't done a
series of various daytime measurements yet..
I want it warmer!
When does heat gain from air temp better the loss from evaporation.
Rough simple approximations is all I require, but probably should
relate water temp to air temp rather than stuff like ..."when its a
warm day"... that depends if you live in Antractica or Manilla!!!!
Thanks to all who have been game to broach this topic -
fascinating!!!!

---

From: Will Stewart <[email-masked]>
Date: Sat, 12 Oct 1996 23:23:07 -0400

> 9,999 times with light bulb filaments.

Then time's a-wastin'!  Submit your patent application and the world
will beat a path to your doorway...

William R. Stewart

---

From: [email-masked] (Nick Pine)
Date: 12 Oct 1996 20:28:16 -0400

>take my cover off if the air temp is warmer than the water temp?????

Perhaps you need less hype and more calculations.

>Forget philadelphia!

Moving your pool to Philadelphia would simplify the calculations...

>This is Brisbane Australia!

Okokok.

>to 26-28 C during the middle of the day and go bback to 15-16 overnight.

Yes... But vot is the hoomidity?

>series of various daytime measurements yet..

Yes... But vot is the hoomidity?
Day/night pool temp probably won't change a lot.

>I want it warmer!

Have you tried lighting 7 kitchen matches per second underneath?
Or just leaving the cover on, unless you want to go swimming?

>When does heat gain from air temp better the loss from evaporation.

When heat loss by evaporation equals heat gain by convection.
That 1926 formula perhaps, with Qe = - Qc. 

>warm day"... that depends if you live in Antractica or Manilla!!!!

How about this, for a crude strategy: bury a glass of water up to its rim
in the ground and put a thermometer in it. When the sun is shining on that
spot, and the thermometer sitting in the glass full of water reads higher
than the pool temp, take off the cover. Not that it will make much difference.

Nick

---

From: Will Stewart <[email-masked]>
Date: Sun, 13 Oct 1996 14:52:11 -0400

Brian K Petroski wrote:
> We can build 100% solar homes with sufficient thermal mass
> of it.  

Of course, earth is an effect insulation, depending on depth and water
content.  

> The house will have solar gain from the southern exposed face and
> summer heat will be pumped into the mound through air tubes. 

What will be the heat storage meduim?  Air, earth, or water?  Have you
considered calculating Qin vs. Qout for an entire season?  How much BTUs
do you plan to store?  I have looked at similar configurations and have
not been able to identify a practical seasonal storage.  Ideally, a
phase change material (i.e., water to ice) can be used in order to
reduce the mass and volume of the storage material. However, phase
change materials usually have a melting/solidifying point that is
favorable for either heat or cold storage, not both.

> In the
> and the times when the air flow runs.  

The southern states tend to have more humidity, hence condensation
problems that promote the growth of mold and other nasty agents.  I
pursued a design using earth tubes and am going with a ground-source
heat pump instead.

> In southern states for example a

You need to consider having two storage mediums, as heat gathered during
the summer needs to stored separately from the cold being used for air
conditioning.

---

From: [email-masked] (Ron Bean)
Date: 13 Oct 1996 15:32:49 -0500

>How about a Monolithic Dome, half full of water, with a houseboat inside? :-)

(ROTFL)

Wouldn't it get kind of humid in there?
I'd skip the dome and the straw bales and just put a pole building over it.
(Just make sure the head has a holding tank...)

I've always wanted to live on a houseboat...

---

From: [email-masked] (Nick Pine)
Date: 14 Oct 1996 07:43:27 -0400

>Wouldn't it get kind of humid in there?

Sure, without a vapor barrier.

>I'd skip the dome and the straw bales and just put a pole building over it.

Sounds cool.

>(Just make sure the head has a holding tank...)

Not necessarily. Perhaps just a stack vent, and a macerator/chlorinator,
with the chlorinator turned off. Wastewater treatment with large warm
reservoirs can be very effective.

Nick

---

From: Brian K Petroski <[email-masked]>
Date: Mon, 14 Oct 1996 12:59:40 -0500

> favorable for either heat or cold storage, not both.

     The heat storage medium will be the earth mound.  I haven't 
calculated out the number of BTUs yet or the exact size of the mound.  
Yes I am fully aware that he mound needed in this climate will be 
considerably larger than the house itself.  I do not consider that to be 
a problem.  Also as I stated, some insulaton will be put on top of the 
mound so it will not loose heat as fast; this in turn will reduce the 
size of the mound needed to store enough heat.

> pursued a design using earth tubes and am going with a ground-source

     I mentioned the souther state idea just as an example.  I have not 
studied the particulars of a warmer climate as my designs are for 
Minnesota, I just wanted to say I felt they can be adapted.

> the summer needs to stored separately from the cold being used for air

     Not at all.  One storage medium, the earth mound.  In the summer the 
mound will be cooler than the air tempurature so it will provide a 
cooling effect by absorbing heat.  After absorbing heat all summer the 
mound will be warmer than the air in the winter and so will provice a 
warming effect.  No need for two mediums, just cooking is in the charging 
stage and warming is in the discharging stage.  There was a concrete dome 
home build in Montana that uses this principle and the owner said that in 
three years he burned only 1 1/2 cords of wood for heat and the interior 
tempurature never rose above 75 degrees even when the summer temps were 
well above 90 degrees.  He then went on to explain where he had made an 
error in his calculations and that the wood heat would be completely 
eliminated by a slight increase in the mass of the earth mound or using 
slightly more insulation over it.

			    Brian Petroski
			Just your stereotypical
			      polysexual,
			       bisexual
			    solitary pagan
		       from St. Paul, Minnesota

---

From: [email-masked] (Nick Pine)
Date: 15 Oct 1996 07:32:01 -0400

Nick Pine <[email-masked]> wrote:
 
> sun               .             .           
>           .                             .            [64 feet long]
>        .b      water     b     water      b. 32" 
 
This would collect about 30% more sun in December, where I live, if it
had a frozen reflecting pool outdoors, to the south.

>under the length of the floor.

As another alternative, the house might have a floating floor.

Some ferrocement barges, perhaps, or some 8' x 16' platforms, bolted together
and wrapped below with a single folded piece of EPDM rubber that comes up to
the top of their 1' sides, with strawbales for insulation, and no air gap
underneath, and solar heat moving into the water via some some air-water heat
exchangers near the top of the greenhouse. If the strawbales had a woodframe
or ties to hold them together, and some chicken wire and concrete on top, the
"platform" below might just be an EPDM rubber bag. 

The heat exchangers could be some fin-tube pipe with a thermal conductivity
of about 5 Btu/hr-F per linear foot, or some used auto radiators with their
electric fans, which might lose the heat equivalent of 1 gallon of gas per
hour, idling on a hot day at 100K Btu/hr/(200F-100F) = 1,000 Btu/hr-F (?),
or some fan-coil units like Magic-Aire's $150 all-copper 2' x 2' SHW 2347
duct heat exchangers, bolted onto window fans, transferring 45K Btu/hour
between 125 F water and 68 F air, ie about 800 Btu/hr-F at 1400 cfm, with
a 0.1" H20 pressure drop.

How efficient would this be, as a solar collector? The solar heat, about
300 Btu/ft^2/hr, max, wants to leave to the colder outside world via the
glazing thermal resistance, which could be R1/960ft^2 in this case, but it
also wants to flow from warmer air into cooler water via the air-water heat
exchangers, so we have something like this thermal circuit, for a square foot
of glazing, where I live, in December, with an average daytime high of 43 F: 

                ------------               Raw
   43 F--------| 300 Btu/hr |->------------www----->---------Tw, water temp
           |    ------------    |  heat exchanger resistance
           |         R1         |
            ----<---www------------Ta, air temp near ceiling
	     glazing resistance

In a circuit like this, current divides according to the conductances.
So if Raw = 1/3, say, and Tw = 43 F, 200 Btu/hr would go into the water
and 100 Btu/hr would go back out through the glazing. If the water were
warmer or Raw higher, less heat would flow into the water.

If the water temp were 100 F, and Raw = 1/8, eg 1 auto radiator for each
8'x16' section of glazing, we would have

                ------------    a          1/8
   43 F--------| 300 Btu/hr |->------------www----->---------Tw = 80 F
           |    ------------    |  heat exchanger resistance
           |         R1         |
            ----<---www------------Ta, air temp near ceiling
	     glazing resistance

So 300 Btu/hr go into point a, of which (Ta-100)/(1/8) flow into the water,
and (Ta-43)/1 flow into the air. So 300 = 8(Ta-100) + Ta - 43, or 
257 = 8 Ta - 800, or Ta = 1057/8 = 132 F, and about (132-100)/(1/8) = 256
Btu/hr flow into the water, so the efficiency is 256/300 = 85%. Using 2 layers
of plastic would reduce the sun by 10% or so, but allow conventional air
inflation of poly film pillows to reduce plastic wind fatigue. It would raise
the efficiency, but double the glazing cost, to 10 cents per square foot.

Nick

---

From: [email-masked] (Andrew McKegney)
Date: Mon, 14 Oct 1996 22:28:09 GMT

>Nick

Hey! Don't forget anaerobic fermentation makes methane! You could tap
the methane to burn in a heater on those sunless days, or for cooking.

Andrew McKegney

---

From: [email-masked] (Nick Pine)
Date: 15 Oct 1996 14:41:40 -0400

>the methane to burn in a heater on those sunless days, or for cooking.

Good idea in principle. You will probably find the numbers show enough
methane for cooking, given, say, a family of 4, and not enough for heating
without the sun, except for a terrifically superinsulated house, but perhaps
enough for cloudy day heating. 

Nick

---

From: Jason Mansfield Roth <[email-masked]>
Date: Thu, 17 Oct 1996 00:12:42 -0400

<[email-masked]>>> We can build 100% solar homes with
sufficient thermal mass
>What will be the heat storage meduim?  Air, earth, or water?  Have you
 
There is a man out west...John Hiatt perhaps (I know that's a rock star,
but I think that's about the name of the builder) who has had success
with such a system (no dome, but an umbrella of insulated earth over a
building). I believe he's in a fairly harsh climate, and gets year-round
storage. The whole principle of earth shelter (even w/o insulating the
earth) is that earth moderates temps and effectively puts the building
in a wind-free 55 degree environment year-round. This makes solar
heating simple with little more than the mass of a cement or tile floor.
Obviously, no matter what your Btu needs, you must have mass to mtach
your glass area or face over/underheating, but the principle is simple. 

Ah, I just checked -- It's John Hait -- Box 4694, Missoula, MT 59806.
And he uses "umbrellas" of insulation over the house (part of the
advantage of this practice -- combine it with a butyl sheet, and you
have a large store of _dry_ earth around your building. It's the cold
water seeping through the soil that robs most of the heat from earth
shelters. Hait also uses earth tubes, hundreds of feet long according to
Mac Wells.

Anyway, hope that insight is helpful. I just want to reiterate that a
basic, well-designed earth shelter should not require much more than a
1/2 cord of wood per year anyway. Add the extreme climate, but subtract
a mass of dry earth, and you should have no problems (question -- how
much sunlight do you get? Frankly, it's the 3 days w/o sun that drain
the mound's heat more than winter in general; in a sunny area, you may
never rely on the mound for more than the temp moderator/wind buffer
that it is).

JMR

93 SL2, blue-green

"I never gave anyone hell -- I just told 'em the truth, and they thought
it was hell."

"What's the use of a good house if you don't have a decent planet to put
it on?"

---

From: [email-masked] (DAVID WILLIAMS)
Date: Tue, 15 Oct 96 10:01:00 -0500

-> When does heat gain from air temp better the loss from evaporation.
-> Rough simple approximations is all I require, but probably should
-> relate water temp to air temp rather than stuff like ..."when its a
-> warm day"... that depends if you live in Antractica or Manilla!!!!

If the *dew point* of the air is higher than the temperature of the
water in your pool, then the pool will certainly gain heat from contact
with the air. If the dew point is lower than the pool temperature, the
calculation is long and complex, involving the temperature and humidity
of the air, wind velocity (including turbulence caused by nearby
buildings) and a bunch of other things. Rather than attempt the
calculation, it would probably be a lot easier to use some sort of
experimental approach, maybe using a miniature "pool" in a jam jar, or
something of the sort, which would warm up or cool down a lot faster
than the full-size pool, so you could see what is happening quickly.
Even a "wet bulb" thermometer, in which the bulb that holds most of the
mercury or alcohol is surrounded by a damp cloth or tissue, might give
you sufficient information. If it indicates a temperature that is warmer
than the pool, take the cover off.

                              dow

---

From: [email-masked] (Nick Pine)
Date: 30 Oct 1996 09:21:34 -0500

Andrew McKegney, "C. E. T" <[email-masked]> wrote:

>The practical answer is very simple.

And in your case, wrong.

>If the sun is shining on your pool and 1.) it is not windy 2.) the air
>temperature is no more than 5 degrees cooler than the pool, you will
>probably  do better to leave the cover off of the pool.

That may work on your planet, Andy, but on an average day in Philadelphia
in October, "solar covers" should be on pools until the still air warms up
to less than 0.04 F cooler than the pool, approximately, a temperature
difference 125 times smaller than 5 degrees (F?). I posted that calculation.
Perhaps you didn't read it, or understand it, or believe it. 

>This is not rocket science, although you can turn it into that if you
>are trying to optimize for the last BTU.

Some people can. Others try to simplify these calculations. C. E. T.s
apparently just pretend they know what they are talking about, and shoot
>from  the hip, with answers that are wrong by more than 2 orders of magnitude.

Nick

With maturity comes the desire for simplicity   --Bela Bartok(?)

---

From: [email-masked] (Andrew McKegney)
Date: Wed, 30 Oct 1996 21:58:35 GMT

>Perhaps you didn't read it, or understand it, or believe it. 

As usual , you jump in not knowing what the hell you are talking about
Nick. You insist on trying to turn a simple approximation into an
exact science. You have not made any allowance for the fact that
having a blanket on the pool blocks between 50 % and 100% (depending
upon the blanket) of the incident sunshine. The biggest factor you
don't even take into consideration in your calculations --- the wind!!

When it comes to answering questions about pool heating with solar you
should keep your ----- nose out of it.

>>are trying to optimize for the last BTU.

And Nick tries to do this to make himself look like an authority, when
he knows NOTHING (by his own admission) about operating or heating a
swimming pool.

Andrew McKegney C.E.T.

Beware of those calling themselves experts

---

From: [email-masked] (Nick Pine)
Date: 31 Oct 1996 11:38:26 -0500

>As usual , you jump in not knowing what the hell you are talking about Nick.

A curious thought, from you.

>You insist on trying to turn a simple approximation into an exact science.

No, but I like to use a little science...
You seem to favour the Wild-Ass-Guess (WAG, vs SWAG) technique.

>You have not made any allowance for the fact that

Let's look again, shall we?

>>in October, "solar covers" should be on pools until the still air warms up
              ^^^^^^^^^^^^^^                              ^^^^^^^^^
>>to less than 0.04 F cooler than the pool, approximately...

A typical "solar cover" might pass 80% of the sun, blocking only 20%, and
might add R1 to the pool surface thermal resistance. Taking that cover off
would add 20% to the solar input and subtract R1 from the thermal resistance,
which might cancel out if the air were cooler than the pool, were it not for
the enormous effect of evaporation, which can make the effective thermal
conductance 50 times higher than an R1 pool cover. 

>...Nick tries to do this to make himself look like an authority...

No. I try to do this to understand how the world works, and help improve it. 

>when he knows NOTHING (by his own admission) about operating or heating a
>swimming pool.

Sometimes knowing nothing is better than "knowing" something :-)

>Beware of those calling themselves experts

Amen.

Nick

---

From: [email-masked] (John Harrison)
Date: Sat, 26 Oct 1996 20:04:32 GMT

>than the pool, take the cover off.

Anything small placed in or on the ground will get a lot of heat
transfer form there won't it? We are talking temps here of 16-17 C at
night and 25-28 C during day.
I am still not sure if the sun is better on the water surface, or
better on my clear plastic bubble cover which is still preventing
evaporation.
I tried exposing half the pool yesterday and measured the exposed
water surface temp vs the temp of water under the cover still - the
same!!! Now maybe thats dumb and the heat transfer is smaller than
1degree.

---

From: [email-masked]
Date: 31 Oct 1996 15:07:09 GMT

Take the cover off before ya dive in!!  Seems simple