Rooftop Air Conditioner

Locate the thermostat inside the store, rather that outside.

Is not the thermostat, located inside the evaporator in the cooling area, as a normal design/practice?

Welcome to CR4.

All temp., I suppose are F ^o

What is the make/type of your Roof-top split AC? Works OK in the summer but at what temp.? Is 50^o - 60^o F not considered cool? What you need, I think, is adequate air change/ventilation in your store. My train of reasoning could be wrong, due to my living in a different clime.

Sounds like you need to escalate the issue to the person who sold you the system, and not let go until you have a satisfactory solution.

What may be happening: 1. This replaces a unit that didn't have an air-side economizer, replaces a smaller AC, or the deli wasn't previously air-conditioned. 2. There is not sufficient exhaust venting for the economizer to make-up enough outside air to maintain the desired inside temperature.

Who on earth needs cooling and dehumidification for personal comfort control at 50-60degF ambient <rhetorical question>? What is needed is simple ventilation. How about switching it off and opening some windows?

OP's mention of 'economizer' makes me believe that his new unit turns off the compressor and opens an outside-air louver to pull in outside air when ambient reaches 60°F. I suspect he doesn't have enough 'windows' open, i.e. exhaust vents.

Similar to my thoughts. It would surely be more efficient to use fans, not the AC compressor. Would have to take care that drafts are not created that will Offend customers, but if done thru the heating/cooling ductwork that should be OK.

AFIK, residential heat pumps commonly have a thermistor near the compressor/condenser coil. When the ambient temperature drops below about 60^oF (~15^oC), it won't allow the compressor to run.

It's worth asking the installer if this is the case on your unit.

Your situation is similar to trying to paddle with your rudder. In the absence of an oar, this can be a useful adaptation, albiet less efficient and causing more wear and tear than using the proper tool for the job.

What am I trying to convey? When outside air temp is below desired inside air temp, what is needed is adequate air exchange. Using your roof top split AC system to attack the problem is inefficient and causes unnecessary wear and tear, but it works for now. You should upgrade ventilation are soon as practical.

sure it can be lowered. you have to remember that the economizer doesn't wok solely off of outside temp. you always have to take humidity into account. you don't want to add moisture you essentially just paid to remove with your mechanical cooling. so yes it can be lowered if you take the right readings and you understand how to program the economizer correctly, good luck

Here is something to consider; if the unit cannot keep the inside of your store cool with an outside temperature of 50 degrees (and inside temp of 78) by simply running the fan only, then there is something wrong with your system. My guess is that the fan isn't blowing enough air (too low CFM) or the vent system has too much resistance.

A fairly inexpensive solution would be to put a large fan on the ceiling (something like a whole house fan). Get a belt drive unit and install it where your customers will not complain about the wind and noise. Maybe in the back room? The whole house fan will pull plenty of air from the inside of the store and exhaust it out the roof. Be careful of negative pressure in the store (you may need to keep a door open). You'll be surprised how quickly the store will cool. IF you don't want to keep the door open, try windows or run the a/c system on fan only.

This solution will be the least expensive, because trying to troubleshoot a rooftop a/c system isn't going to be cheap.

Good luck and let us know what you do.

Thanks. I really got a lot of help from the Forum Thread. Now I know that I have to install a vent or two for the heat to be vented out. My deli store is divided by the front store and kitchen in the back where there is even more heat generated by ovens and two walk-in coolers. The space above drop ceiling is open in the whole area, so the heat from the kitchen goes to the front store above the ceiling. My plan is to install two vents, one above the walk-in coolers in the back and another in the front to remove the hot air gathered above the drop ceiling. I believe that the biggest problem comes from a poor design of the heating & cooling system which wasn't modified when the space was converted from an office to a deli store years ago.

I'm not a ventilation engineer, so squawk if I'm wrong. If possible put the new vents on the downwind side. In order for hot to vent out, makeup air has to come in someplace--does that place exist? It might be preexisting leaks. Remember that this make-up air will be outside temperature, and will have to be conditioned.

To much talk and no action! Get the unit name plate data, include the economizer also. The problem is not hard just lower the economizer switchover point to a temperature that matches the discharge air temperature when the A/C is running. The equipment may not have come setup to do this, but without the data no good solution can be found.

HAVE A CONTROLLER WITH A WIDER RANGE INSTALLED IN ORDER TO HAVE THE ECONOMIZER SUPPLY 55 DEGREE AIR. iF YOUR SPACE IS COOLED TO 78 WITH 60 DEGREE AIR, 55 DEGREE AIR SHOULD GIVE YOU A SPACE TEMPERTURE FIVE DEGREES COOLER...73, A VERY CONMFORTABLE TEMPERATURE. ACTUALY, 78 ISN'T ALL THAT BAD IF YOU ARE IN A DRY CLIMATE, SUCH AS DENVER, COLORADO.

LOU BINDNER

fresh air make-up vent is too small and your building is too tight.

You need a way to relieve the pressure buildup inside the building when outside air is below 60 degrees and your unit is pulling in fresh air instead of re-circulating cooled air. Someone didn't have their Duct-U-Lator with them the day they installed the fresh air make-up vent.

http://compare.ebay.com/like/290762941371?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

Also, you don't say if you have a cooktop hood running all the time. If so it is pulling all the new cool air right back out before it can circulate in the room.