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Cooling load, heating load, sizing equipment

Guys and gals, I'd love some of your advice here.  Please give me your thoughts.

I'm the property manager of an old church in Chicago.  6,800 square feet in the sanctuary including the entrance/vestibule and 1,000 square feet in the balcony.   We want to install AC in the sanctuary.   In the beginning we hired a mechanical engineer to look at our building and give us some options on equipment.  He gave us 3 options with mechanical specs, layout of equipment, wrote up an RFP for us, schedule for submitting/receiving proposals, etc.   A. Roof top units B. Chillers C. Geothermal.  He told us we need 40 tons of cooling.<img src="https://mail.google.com/mail/u/0/images/cleardot.gif" width="1" height="1" alt="" />

We got some bids, the geothermal bids actually came in lower than the other bids. Almost all of the contractors who've come in here have said 40 tons of

cooling is too much.  One guy said less than 30, another said maybe 25 is enough.  One contractor brought a internationally certified geothermal installer and he said our cooling load is less than 30.  Many of you know Dave Bunnell, he said even less than 20 would be enough to cool our sanctuary. .

I finally got smart and asked our engineer how he came up with his load calculations and asked for his calculations.  He's going to get the calculations and data to me hopefully next week.  I asked him to briefly explain his method of load calculation: 

A.  He said, we calculated your cooling and weighted heavy on your seating capacity.  We weighted 80% to 90% on your seating capacity.  We weighted 10% to 20% on your building envelope.  We had to do some guess work on the building envelope.  (This all made sense to me - somewhat.)

B.  He said, we calculated your heating load based on the current size of your boiler.  (This doesn't make sense to me)

Here's where I need some help and would love your feedback:

1.  What are your guys thoughts on our engineer's approach to calculating cooling and heating load?  Is this standard in the industry?

2.  Should we hire an energy audit company to come in and give us a very precise calculation on our true cooling and heating load and perform an energy audit of the whole building?

3.  If yes on 2, do you have any recommendations for companies that can give an audit for a large commercial building such as ours.

4.  Should I do my own simple cooling load calculation?  Is it difficult?  If I buy the software or  use the old method by hand, can a lay person do it?  Even though I'm pretty stupid for not asking for the load calculations months ago, I'm pretty savy on computers, I have a basic understanding physics, thermodynamics, HVAC.  I have the desire to calculate this, can I do it?

5.  Should I hire a trusted HVAC guy I know (he is one of the contractors actually who came in 2 years ago and said we'd only need 20 tons of cooling.  Should I hire him and pay him hourly to come in and walk me through a cooling load calculation?

Thanks again...


  • Rich_49
    Rich_49 Member Posts: 2,763
    In Illinois

    Contact Corbett Lunsford at Green Dream Group .  He will know who to put you in contact with and your best avenue to achieving your goal . He will also have vetted anyone he recommends prior
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailor
    icesailor Member Posts: 7,265
    Cooling Loads:

    I don't claim to be any kind of expert in this area.

    I think that your ME hit the bases. Except in one area. Sizing the heating load by the boiler size.

    Where I believe the cooling load comes in and the ME might be correct is his estimate of adding 800 people to the cooling loads. When you have a room full of 800 people, you don't need heat, you need cooling. Adding the heat gain of 800 people isn't something that internationally respected Geothermal people consider when doing a residence with 4 people living in a 6,000 Sq. Ft. Cottage. They usually don't have a lot of personal experience with the design of places of public assembly. Something that licensed ME/LPE's usually have specialty training. Trust me.

    Its my understanding that Chicago in the Summer time can make Florida seem like New England. When you get 800 people seated on Sunday on a hot humid summer day, you might be needing every pound of that 40 tons. In January when it is cold in Chicago, which still gives New England a run for the temperature money, and you have 800 people sitting there, the boiler is too big. But 3 hours before they get there and 6 hours after they leave (the 800 people), it's just right  or a tad too big. But when those same people are sitting and sleeping on Sunday, you might need to use some of that 40 tons to keep them awake. People, tend to get sleepy when they become overheated. And they don't get the message they paid for with their donations.

    Who is right and who is wrong? I don't know. I only know that it takes a lot of cooling anytime to equal the BTU heat load given off by 800 concentrating people. The more they think, the more heat they give off. Or so I understand.
  • SWEI
    SWEI Member Posts: 7,356
    Sensible and latent loads

    are calculated separately.  I'm not sure where the "80% to 90%" numbers came from, but maybe that works in Chicago.  There is more than one way to remove humidity.  I'm sure Rich's guy is familiar with all this.

    The complete lack of cluefulness demonstrated on your heating load makes me question the whole deal.
  • GP
    GP Member Posts: 25
    edited June 2014
    capacity / attendence

    SWEI, icesailor and all.  I should clarify.  Our Max  CAPACITY based on our building structure, exit sizes, number of exits, etc. of 500 (in the sanctuary) and 50 (in the balcony) per the city of Chicago.   This is what Chicago says we can haee

    IF - and I don't know yet, but IF our ME calculated his cooling load on Chicago max capacity, then it's wrong.  And this is what I'm waiting to find out from him, what number of people he used.    The truth is, I don't remember him ever asking me for attendance numbers - we have them for every Sunday for the last 8 years.

    The reality of it is WE WILL NEVER HAVE 550 PEOPLE!  (not yelling at you...throwing my hands up in the air and yelling at myself and our ME).  We can't even fit 500 people in our pews!  Above 300 it gets very uncomfortable.  Our pews only seat so many people comfortably. 

    Our typical attendance on a Sunday is - at this is in the winter. 

    100 or less for the first service.  (9:00 to 10:15 am)

    180 to 220 for the 2nd service.  (10:45 to 12:00 noon)

    In the summer our attendance drops (yes, maybe because of the heat, summer vacations, etc.)

    The most we've had in the last 10 years is 375 people for a 2nd service Easter.  And as one of the other property committee members just told me yesterday - that's in the cold season!

    So 220 people in 7000 square feet (granted 53 foot ceilings), but 40 tons.  Does that seem too much?

    Rich, thanks, I'll give Corbett a call Monday.
  • coolintg calcs....

    You don't need to provide cooling for that 800 people when they are only there for an hour or so, particularly in the morning.  The mass of the structure will absorb heat and your solar gain has not built up for the day.   When you run a full ASME cooling calc that takes into account length of occupancy, mass of structure, time of day, and the activity level of the occupants   the cooling loads drop enormously for a typical church setting.    The last church I ran the calcs on ( about 6 pages of numbers) had about 120 on a Sunday morning for a single 1 hour service in a high mass building and only needed about 6 tons of cooling.  It's been in use for ten years and works just fine.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
  • icesailor
    icesailor Member Posts: 7,265
    Cooling loads:

    I wasn't saying that the heating cooling loads were wrong or right. Just that many don't realize how much heat a person gives off when just sitting there. Each and every person in a room is just another little radiator.

    To me, it sounded like some were using shortcuts and that your ME might be on the mark. They tend to be more conservative because they have different liability that some estimator from XYZ HVAC Company.

    You've asked good questions. Sitting down with them will allow you to separate the bull from the pucky.

    What The Steam Pro says is absolutely on the mark.

    I've never seen it written, but I think that there is a whole science to climate control in large structures where you need to heat up the building for when people arrive, but shut off the heat before they get there. And then using AC/Ventilation for when the people start heating the space with body heat.

    Where I used to live, they built a new high school with a new Auditorium  to have public meetings in. If they filled the building in Fall, Winter or Spring, it would overheat sooner or later and people would start falling asleep. Maybe from CO. But if the the building overheated, they either never turned on the AC or started the ventilation system. Its a science and art.
  • don_9
    don_9 Member Posts: 395
    Fresh per person

    What I think you are missing is the fresh air requirement that in most cases I've seen doubles the cooling load. Keep in my co2 is a issue and you need so many air changes an hour per code, however you need to think of humidity its there in the winter as well as it is in the summer. We deal with humidity in the winter with fresh air and in the summer with the cooling equipment.

    Also when dealing with fresh air you need to activate the fan when the people are there thru some type of device that can monitor the co2 levels.

    From where I am sitting and being nothing more then an armchair quarterback I am going to have to side with engineer on this one.