Subject: Re: Floor Water Heating

From: [email-masked] (Will Stewart )
Date: 9 May 1995 14:28:39 GMT

In <[email-masked]> [email-masked] (tpereira) writes: 

I'll take a stab at these;

>will a 1/2" water pvc pipe @1' ctc under tile/earth floor store
>enough heat from a solar heat panel ? 

You need to know;

    1.  How long is the pipe?
    2.  What is the R value of the pipe?
    3.  What is the temperature of the water entering the pipe (and        
    exiting)?
    4.  What is the temperature of the tile/earth floor?
    5.  What is the R value of the floor?
    6.  What does that heat exchange layout look like?
    7.  What is the volume and specific density of the floor material?

As you can see, this is not an easy question to answer.  As few of the
temperature values above are static, calculus should be used in order to
more properly model the energy system.  However, you will probably not need
to create a system with close energy storage tolerances, so some simple
equations might help (with the above information).

>what heat transfer equations should I use to calculate btu's ?

The simplest equation is 
                              delta T
                         Q =  -------
                                 R
where Q = Heat exchange rate,
      R = Insulation value
      T = Temperature (delta means "change" or "difference")

Take a look at some NREL fact sheets, for example;

http://nrelinfo.nrel.gov:70/0h/web_info/documents/erec_fact_sheets/2.ht
l

>are the thermal conductivity properties
>of pvc adequate, or is pvc too much of an insulator ?

I would say adequate, if you use enough length.  Use the information
above
to perform your calculations.  A good thermodynamics book will have the
R-value.  (I just don't have mine here at work)

>will pvc deteriorate/break/leak with age ?

What kind of liquid will you be using?  Check to see if it reacts with
PVC. Some PVC piping in my area is breaking down after 20 years of
exposure to highly chlorinated city water.

>will pvc outgass ?

Probably.  Use a air-to-air heat exchanger to bring in fresh air.

Do you plan to air condition your house?  Note that this system, if
used with cold water, can cause condensation on the floor if used in a
humid environment.

Hope this helps,

Will Stewart

---

From: [email-masked] (System Administrator)
Date: 9 May 1995 16:56:41 GMT

tpereira ([email-masked]) wrote:
: will a 1/2" water pvc pipe @1' ctc under tile/earth floor store
: enough heat from a solar heat panel ? 

Don't use PVC.  The stuff designed as plumbing pipe is only good for
cold water.  Cross linked pvc (CPVC) is ok for hot water, but you have
to use cement, and joints -- not a good idea for something embedded in a
floor.

Polyurethane I think, or poly butadiene (spelling?) is the usual for
this application.

: what heat transfer equations should I use to calculate btu's ?

Grab the ASHRAE handbook at your public library.  Every possible
equation concerning heating and cooling, with lots of tables for those
who aren't good at calculus.

: are the thermal conductivity properties
: of pvc adequate, or is pvc too much of an insulator ?

They are adequate, if you have enough pipe in the floor.

: will pvc deteriorate/break/leak with age ?

Yes. PVC has solvents in it to keep it flexible.  One of the reasons
either of the above will be better.  Polyethelene may work too, but be
sure it's rated for the temperature you will have. (polye is basically a
giant wax molecule -- one of the least harmful plastics we make.)

: will pvc outgass ?

Yup. Go open a box of plastic sheet protectors and take a big sniff.

--
=> Sherwood Botsford                   [email-masked] <= 
=> University of Alberta         Lab Manager, Space Physics Group <=         
=> tel:403 492-3713                             fax: 403 492-4256 <=