Electrical Engineer

Google: "sizing air conditioners".

I'd get some professional help if this is your first job sizing air conditioners. What will happen if you need to size one and don't have a computer handy to get someone to do your job for you?.

Call an HVAC supplier/designer/installer who will quickly and easily size a system for you in the hope of a sale.

Your right to ask the question. As an engineer who used to work for Carrier Air Conditioning, you need to know that the price you pay is by the TON, (12,000 btu's).

If you oversize the unit, you're paying too much for the unit and the installation. If you buy a unit too small, it will run all the time and your customers will be hot and uncomfortable.

http://www.gartnerhvac.com/airconditiongcalculator.html

Attached is a web site where you can download a calculator that will help you determine the correct size for your needs.

That done, have a pro do the same thing based on the fact you're going to buy from them.

Compare the results. If there is a big difference, find out why. If not, you know you made the right choice.

Good luck

Laby

Hi there, My name is John R. Fairchild CMS. I am a professional in the HVAC/R field with many years of experience. The first thing that you need to do is ad up all of the electrical loads in the space that you're going to cool (lighting, computers, cash registers, TVs, refrigerators, freezers, microwaves, etc.) Take the total wattage of all these loads that are likely to be on at the same time and multiply it by 3.42. This gives you Btus to add to the rest of your load. Then estimate the maximun number of people that will be in the space at any one time and multiply it by 500, then add it to the first number. If it is a restaurant you'll want to add at least 25% for the heat and humidity load of the food itself. Also if it is a place that has an exhaust hood you'll want to add some to your infiltration loads to allow for the hot humid air replacing that which the hood pulls out. Find out how many CFM it pulls out and if you have any makeup air coming in through a makrup air unit, as these will have a direct bearing on the load calculations. Next you'll want to know how good the insulation on your walls and ceiling or roof are, as well as the thermal ratings and sizes of your windows and doors (orientations are VERY important (N, E, SE, S, SW, W). And last but not least, what temperature do you want to maintain inside, and at what outside temperature would it be acceptable for it to start rising. Of course the square footage of all walls ans windows is important, along with the roof. Also does the space share a wall with another tenant and is that area conditioned or not? As you can see there are too many variables to consider to get an accurate estimate of your loads without a thorough onsite inspection. That being said, if you do your homework, you can avoid a poorly performing system in most cases. And by showing your figures to a few contractors, observing thier reactions, and checking out thier references, you'll be well on your way to getting a good job done at a fair price. Beware if one contractor comes back with a lower price and his equipment is smaller in capacity, you might ask to have him show you his calculations and explain them. If he can't, run the other way! (712) 592-0844 If you have any other questions feel free to call me, John