[BLDG-SIM] DOE2.1E Heat recovery question

[Michael Brandemuehl]

Dominique,

The issue of refrigerated cased in supermarkets is messy. Physically, the
net total and sensible cooling effect on the supermarket zone (sometimes
called the "case credit") are driven by heat and mass transfer from the case
itself, and therefore is dependent on store temperature and humidity. Cases
are typically rated at 75 F and 55% RH store conditions, but the latent
cooling effect of the cases is particularly sensitive to indoor humidity.
The sensitivity is different for low-temperature and medium temperature
cases. However, most of the models calculate the cooling effect as the
difference between the average compressor load and the internal case heat
gains, including fans, lights, and anti-sweat heaters. Depending on case
design, these heat gains can be surprisingly large. In addition, the
compressor capacity will naturally be oversized to account for product
pull-down.

I would suggest two sources of info. First, ASHRAE sponsored Research
Project 596-RP Effects of Indoor Space Conditions on Refrigerated Display
Case Performance. The work was completed by Ron Howell in 1991. I expect
that the final report can be obtained directly from Bill Seaton at ASHRAE.
Second, EPRI has done quite a bit of work in this area. They have also
developed a computer program call SST - Supermarket Simulation Tool.
However, you may have difficulty obtaining the reports if you are not
affiliated with an EPRI member.

Good luck,
Michael J. Brandemuehl, Ph.D., P.E.
Civil, Environmental, and Architectural Engineering
University of Colorado
428 UCB, ECOT 441
Boulder, CO 80309-0428
303 492 8594
303 492 7317 fax
michael.brandemuehl at colorado.edu

-----Original Message-----
From: postman at gard.com [mailto:postman at gard.com]On Behalf Of Dominique
Michaud
Sent: Tuesday, July 31, 2001 9:31 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] DOE2.1E Heat recovery question


>From the DOE2.1E Supplement:

REFG-ZONE-LOAD	is the total cooling effect...

			Manufacturers of supermarket cases usually do not
list the
			total cooling effect of their cases directly.
Instead, they list the
			compressor capacity at a standard suction
temperature
			required per lineal foot of case work. The sensible
cooling effect
			is typically 65% of this number, and the latent
cooling effect is
			about 10%. The total cooling effect is then about
75% of the
			listed compressor capacity per lineal foot,
multiplied by the
			lineal feet of case work.

Does this mean that 75% of the compressor's cooling capacity cools the zone?
Where does the other 25% disappear to?
Do these figures vary depending on ambient conditions?
Are there any references for these numbers (ASHRAE or otherwise)?

Any and all help is greatly appreciated.

Dominique Michaud
Building Energy Technician
Dessau-Soprin Inc.
375 blvd Rolland-Therrien, Suite 400
Longueuil, Quebec, J4H 4A6
Tel.: (514) 281-1033 ext 2568
Fax: (450) 442-9996


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