Subject: Re: Off-Peak A/C with Ice Storage?

From: [email-masked] (ACADManR12)
Date: 5 Oct 1995 22:47:24 -0400

My company recently installed such a system in a large school and I have
designed similar systems for large commercial applications.  The problem
with an ice storage system in a residential application is the associated
costs of the new equipment required to convert the present AC system from
DX refrigeration to chilled water.  Not only would it require new coils in
the existing furnace or a new furnace itself, but the existing condensing
unit would not function as a proper chiller to make ice.  The cost payback
of a proper ice storage system would be in the range of 75 to 100 years
and this would not be good money management.  

A better solution would be to install a programmable thermostat.
ACADManR12

"Please Lord,   All I want is a day off!!"

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From: [email-masked] (William Bahnfleth)
Date: Fri, 6 Oct 1995 16:06:07 GMT

ACADManR12 wrote:

>The problem
>DX refrigeration to chilled water...

Not true.

Quote from Lennox "TES Update" dated January, 1995:

"The multiple-patented Lennox Cool Thermal Energy Storage (CTES) concept was 
developed to reduce on-peak electric power demand due to air conditioning...

To meet these objectives, the Lennox CTES concept is an _all_DX_ 
refrigerant-based design (no secondary circulating fluids) that integrates 
with the HVAC system refrigeration circuit providing three distinct modes of 
operation:

Direct cooling at system ARI rated efficiency.
Ice making.
Ice discharging cooling."

This is the equipment I mentioned seeing at the equipment show in Chicago in 
January.  As I stated previously, the problem with residential storage is that 
most rate structures don't include demand charges.  Therefore, without utility 
incentives to prop up the technology, it has no economic advantage over less 
expensive conventional systems.

Bill

--
William P. Bahnfleth
Department of Architectural Engineering
Penn State University-University Park
[email-masked]

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From: [email-masked] (William Bahnfleth)
Date: Mon, 9 Oct 1995 14:35:54 GMT

JAYW773 writes:

>In article <[email-masked]>, [email-masked] (William Bahnfleth)
>writes:

>Are you saying that the air stream comes in direct contact with the ice? 

The ice is static and refrigerant tubing is immersed in it.  The discharge 
operating mode involves "pumping" refrigerant through the ice module and 
cooling coil, so there is no direct contact.  However, it should be possible 
to produce lower supply temperature with this system just as is the case with 
other ice storage systems.

>> As I stated previously, the problem with residential storage is that 
>>most rate structures don't include demand charges...

>What about areas where the electric utility charges residential customers
>time of day rates with the electricity being less costly at night but
>customers still having no peak demand charge.  Do you think that this type
>of thermal storage would be cost effective?

Yes, this would provide an incentive--but you'd have to run the numbers to 
determine whether it's economically feasible.  I imagine that the combination 
of a meaningful TOU differential, better ambient conditions for an air-cooled 
condenser, and less part-loading of the compressor could add up to a 
significant difference in operating cost.

Bill

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From: [email-masked] (JAYW773)
Date: 8 Oct 1995 22:24:40 -0400

Are you saying that the air stream comes in direct contact with the ice? 
This system seems quite interesting.  Do you know if this type of system
actually results in a lower space humidity when in operation?  This would
be another selling point of using this type of  system.  

>expensive conventional systems

[email-masked]

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From: William Stewart <[email-masked]>
Date: 20 Oct 1995 20:13:30 GMT

>expensive conventional systems.

What about the occurrence of lower temperatures at night?  Wouldn't this provide 
an opportunity to take advantage of lower ambient temperatures?  Of course, extra 
losses have to be taken into account.  Does Lennox reference any studies or 
estimates?

-- 
William R. Stewart, Jr.		[email-masked]
DEIS Technical Team		(703)760-0239
Application Development Lead

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From: [email-masked] (William Bahnfleth)
Date: Mon, 23 Oct 1995 00:13:55 GMT

>>with the HVAC system refrigeration circuit...

>losses have to be taken into account.  Does Lennox reference any studies or 

I don't know about this particular system, but prior studies I've read 
indicate that you would be doing well to break even on energy consumption 
between daytime air-cooled DX at "conventional" supply temperature and night 
ice making duty with a lower evaporator temperature offsetting the benefit of 
lower condensing temperature.

The Lennox bulletin I have gives an example in which a conventional system 
consumes 19,300 kWh during "summer" operation (whatever that means) while 
their TES unit consumes 20,942 kWh (8.5% more).  No other studies are 
mentioned, published or otherwise.

I suggest you contact Lennox in Dallas if you are interested in pursuing this 
further.  Incidentally, I haven't seen much mention of this product since the 
show, so I have no idea whether it is having any success in the market.

Bill Bahnfleth