I have a response but note that my response is *speculation*, but here goes.
My guess is that the difference between compressor load and total cooling effect is actually the difference between evaporator load and total case load per hour. When I was in refrigeration school, over two decades ago, I was taught to size the refrigerated case evaporator so that the daily heat gain can be met by 16 hours of evaporator run time per 24 hours. The reason for this was to allow sufficient time for off cycle defrost. Have not kept up with modern refrigerated display cases, so do not know if the schooled methodology is still appropriate.
This brings up an important air conditioning sizing issue for supermarkets. ASHRAE recommends HVAC designers take into account the heat absorbed by refrigerated display cases when running heat gain/loss calcs. Unfortunately, ASHRAE offers no guidance for imperical hourly heat absorption by the display case verses the evaporator load.
For a recent supermarket commissioning project, the HVAC designer assumed 16 hr/day evaporator sizing, thus the heat absorbed from the space was 2/3 of the scheduled evaporated loads. This was further multiplied by another fudge factor, since the designer was hesitant to assume net heat absorption to space as 2/3 of scheduled evaporator load, which seems reasonable to me.
Hope this helps.
Dominique Michaud wrote:
>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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