Cooling load question.

Mark Eatherton

I am performing an energy audit on a potential clients restaurant at a Colorado Ski resort. I've done the math associated with the conductive heat losses and infiltration, and am in the process of backing out the known internal gains to come up with a net needed balance that will be provided by the windows.



The only item still in question is the heat generated by the reach in coolers, refrigerators etc. In my hydronic minds eye, the only time that those refrigerant units would actually produce sensible heat is when they are filled with produce/meats etc. that need to be cooled down to their required storage temperature. For the balance of the time, the refer's are basically recycling heat that has worked its way into the inside of the box, correct?



In other words, I should NOT take into consideration the heat generated by the coolers, because of its transient nature, and the fact that it is basically recycling internal heat.



Or do I need to add the motors (compressor and condenser fans) heat in to the gain mix?



Now that I'm retired, maybe I'll go back to school and study refrigeration :-)



Thanks for any input (pun intended)



ME

MarkPFalade

Yes,

you do need to consider the load created by the motors. I don't know what program (if any) you are using but I still use Horgan's Omnicalc and it has generic lists of this type of equipment and their resulting BTU outputs, Not perfect because you can't include everything there is out there on a list but they will at least put you in the ball park. Another very important consideration is the load produced by the exhausts over the cooking equipment, grills, fryers ovens. The most correct way to approach cooling and heating a resturant kitchen is to first calculate the correct amount of exhaust leaving, ensuring that the air will be made up from outside and the incoming air must be conditioned. Reznor produces make up air equipment for this but be forewarned, it not be cheap. I just did a calc on a small one myself and the unit necessary with it's accompanying price nixed the deal. Naturally they wanted me to do it cheaper but I told them cheaper wouldn't work and I would not be willing to put in anything that wasn't designed to do the job adequately. They wanted me to put in a recirc system. Recirc will not work correctly, all the cool air gets sucked out and is replaced by outddor air continually. Here's a place where the guy spent $500,000 on kitchen equipment but refused to spend just a small fraction more to cool it adequately. Beautiful kitchen, hot as Hades in the summer. Why tell you this? So you'll bid it correctly and be willing to turn away when they want you to start cutting corners.



Oh, rereading says you are not calculating for an install just an audit? Sorry I read a bit more into that than you were looking for.

MarkPFalade

Refrigeration is easy...

it's just a spray can that captures the spray, re-liquifies it and put's it back in the can. ;-)

Tom Blackwell_2

Parasitic loads

Mark; I have always used the heat of the fan motor and any other parasitic load times a percent-on time for these systems, say 50%. You are correct that any heat through the freezer or cooler envelope comes from the surrounding space and should cancel out. For freezers with electric defrost try figuring on a 10 minute defrost cycle every 6 hours-the defrost kwh energy stays in the freezer and must be removed.

Mark Eatherton

Thanks Tom...

Still and ALWAYS learning :-)



ME

Techman

Heat Input

Hi Mark,a little late on this one.Yes you do have to figure in some extra BTU's from refrigeration units due to the evap fan motors {24 hrs a day], some have door anti sweat heaters ,refrig/freezers,;then there is the ice machines; then there is the condensor fan motors; then there is the 15% factor that takes into consideration the electric produced/ provided btu's from the "heat of compression" of the compressor. ALL condensing units AC/ REF/ FREEZER /ICE SYSTEMS reject more btu's than the evap coils pick up.Then there is the exhaust/ intake air units,they almost always exhaust more air then they bring back in.And some kitchens have real hot "food warmer lights"This is for the next time I hope.Some commercial freezers have 3-4 defrost cycles of 15-25 min's depending on ambient humidity/door openings/