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Cooling Load Calculator for RTU

Cooling Load Calculator for RTU

Cooling Load Calculator for RTU

Hello All:

Can somebody recommend and online calculator resource or free software to run some basic cooling loads for medium sized church in Dallas Texas.

Thanks a lot.

RE: Cooling Load Calculator for RTU

Hire an Engineer familiar with HVAC

RE: Cooling Load Calculator for RTU

As Willard3 said, you need someone to help. There is no basic load for a medium sized church. People, windows, etc all contribute to the load, but the use here is probably intermittent. Local codes may allow for things like ventilation air to be treated differently if the space is only occupied to capacity for a few hours per week. You could be way off trying to wing it.

I don't know of any free software, by the way, other than those that might be given to HVAC engineers by the big manufacturer's reps like Trane and Carrier.

RE: Cooling Load Calculator for RTU

a typical rule of thumb for residential, which is usually better insulated, would be 1 ton/700 sq.ft. say your "medium" church is 500 people, and say they're all actually awake, but mostly sitting and relaxed, so 100 W/person --> 50 kW of heat generation --> 14.3 ton of cooling for the body heat load alone.

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RE: Cooling Load Calculator for RTU

Residential "rules of thumb" are useless for a church. It's a whole other ballgame.

If you do happen to find a free online load calculator, use extreme, extreme caution. More likely than not, to be free they are not up to date with current code ventilation requirements, offer only block load calculations, are limited in system options, have limited wall/roof/window libraries or any combination of these factors. Last time checked, they were almost exclusively geared toward residential applications.

I'll double down on my comment that a church is a whole other ballgame from a residence.

I agree with Willard and BronYrAur, hire an HVAC professional engineer for the job.

RE: Cooling Load Calculator for RTU

@BronYAur Thanks for your feedback. In fact I have experience designing systems for residential, restaurants (hoods type I and II) and commercial projects (more like strip malls) using ASHRAE guidelines. As you mentioned, a church with an outdated system needs to account for people, assuming full capacity taking into consideration IMC's CFMs and OA reqs. My post come from an intention to find an efficient, yet rational system that is not overdesigned but that allows for a contingency capacity for very hot Dallas days like the ones we are having right now. I just found a very nice speed sheet in excel from ACCA that takes into account occupants, building enclosure, orientation, infiltration and geographical location and like it so far more that what I have used before.

@IRstuff, thanks for the figure, will consider it.

@dbill74. Thanks for your comment, forgot to mention my background, lately involved on a lot of HVAC design upgrades, restaurants, kitchens, and fixups and excited to design rational systems that take into account all considerations. Not really looking here for a shortcut, as I personally dont like them. Maybe my original post was misleading. Yes, my strength is structural, but HVAC endeavours are coming in strong due to market. Best! I have been in Texas only two years right after licensure.

Thanks to all who made intelligent, contributing responses to my original post.

RE: Cooling Load Calculator for RTU

If you are doing more HVAC projects, purchase HAP, Trace or other load software. Yes its costly but with training (also costly), you will use it. IMC and energy codes now require loads to be run. You get what you pay for so pony up and do a purchase. I see it the same as CAD software or scanner/plotter. These are the tools of the trade. You may get by with a light block load vs full simulation. I ran my first loads on punch cards on Trace. The software really shines when it comes to system evaluations. You can help the project team with the envelope and payback. Do the correct engineering math to show why you are better than the guy that guessed. Your simple church is not that simple after all based upon CO2 reset , SZVAV or pull down options.

RE: Cooling Load Calculator for RTU

The cooling load calculation must take into account the schedule of church services to properly profile the people occupancy load and not oversize cooling equipment. After calculating thus compare with the rule of thumb below for churches as published in HVAC Equations, Data and Rules of Thumb by Arthur A. Bell Jr.

Total Heat 0.04 - 0.06 Tons/Seat
Total Heat 480 - 720 Btuh/seat
Room Sensible Heat 260 - 330 Btuh/Seat
SHR 0.65 - 0.75
Air Flow 15 - 30 CFM/Seat
Air Change Rate 8 - 15 AC/Hr

RE: Cooling Load Calculator for RTU

Bell is a great book, but giving somebody that doesnt know loads, a bunch of rule of thumbs, can really get them in trouble.

knowledge is power

RE: Cooling Load Calculator for RTU


I'm guessing you attend this church and want to help them out to avoid engineering costs. Do so with caution. Although the church may save money on the design, they may pay for it several times over with a poor end result. This could be any number of things. Oversized equipment that cycles to often and won't stand the test of time. Undersized equipment that won't handle the load. Or just a cheap installation that doesn't consider the application. I have seen fan coils literally hanging from the walls of old church sanctuaries. They were loud and set to have the fan cycle with the condensing unit so that it was extremely noticeable. That is the last thing I would have done. One of the challenges of a church is to hide the equipment so that you don't see it, hear it, or feel it. A church member in the HVAC business might not necessarily take all of this into account. I'm sure cash is tight, as with any church, but spend it wisely by starting with the correct design. An stay on top of the engineer you hire to make sure it is a quiet system that is hidden as well as possible.

RE: Cooling Load Calculator for RTU

I will again recommend hiring an Engineer who is familiar with HVAC.

A church is not a simple system and "rules of thumb" will bite your butt.

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