How To Size A/C For Elevator Equipment Romm 3

[trocque]

I'm working in Chicago and have been tasked with sizing the proper system for a three 10,943 lbs capacity elevators. The elevator equipment room is approx. 800 sq ft in size, with brick walls, and it is on the 18th floor.
How do I determine the size and type of unit to install?
The customer wants to have a 42,000 Btu split heat pump system installed (he wants supplemental heat in the frigid winters). I told my boss that I didn't think a heat pump in Chicago winters (weeks on end it can get well below 0 degrees) was a good choice. Also, the customer does not want the outdoor condenser to sit on the roof, it must be mounted on the side of the elevator room outside wall. This means that he has a residential split system in mind. Is this possible? Is this a good decision?
So, if someone could tell me how to take a proper load count on an elevator room (i.e. does one need to take the HP of the motors into consideration) and what the most prudent system configeration would be, I'd be verygrateful.

 

[trashcanman]

Use a ductless split system heat pump. The elevator equipment does not have to be at 75 Deg.F. The electronics would love freezing temps. Calculate heat produced by the motors via ASHRAE's method. Assume a 50% usage factor. Probably 2.5 tons would be plenty. The ductless splits can throttle way down to probably 25% of capacity.

 

[DuctHunter]

The elevator manufacturer should be able to tell you what is the heat gain to space is of the elevator equipment and what the maximum space design temperature should be. That is the quickest and most accurate way to get the information. I always contact the elevator company for this information instead of guessing at it. Generally the elevator equipment room should not need to be heated in the winter time as the equipment from the elevator will be putting out heat to the space. Heat pumps can work in Chicago, but their heat output capacity in the winter time drops drastically once the temperature drops below about 30 degrees and typically the cost of the heat pump doesn't have a good payback because there are too many cold days in the winter in Chicago. Why not explore an split system for cooling with electric wall heater in the winter for heating. My guess is the odds are you won't need to heat the space so the electric heater will not be used, but it is there just in case and it is cheap too.

 

[trocque]

Thanks to the both of you!

I have already cautioned my customer about using a heat pump in Chicago winters. Initially I had suggested a mini-split with 3 tons of cooling and to supplement the heat during the winter with electric heats; however, I was talking with a mechanical engineer colleague and he suggested that I install a Bard 3 ton 15 kw 230/3 phase wall mounted self contained packaged unit. He believes these sort of units work better in this application and and then there is the option of running a supply and return duct if we wanted to distribute the air more evenly. What are your thoughts on this?

 

[DRWeig]

I'm a big fan of the Bard units -- we find them in schools all over the country. That sounds like a good solution as well. (I'm not a Bard rep). They just seem to be really durable in the cold climates and they have an exhaust recovery ventilation option that makes good sense in Chicago.

Best to you,

Goober Dave

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[trocque]

Thanks for your in put...I'm not too familiar with Bard products, and having another engineer who endorses the product makes me more confident in suggesting the product to my customer. And to be clear, I am not a Bard rep. and am note endorsing the product over anything else. Just trying to find the best solution for my client. I apologize if my mentioning Bard vilolates the forum rules...please advise on this.

Tim LaRocque

 

[DRWeig]

Yes, we try not to endorse -- but since you specifically mentioned Bard as a possibility, I threw in my opinion. There are other good ones too. If you decide you don't need any ventilation air except what you get from infiltration and stack effect, perhaps a ductless split system would be a better value.

Best to you,

Goober Dave

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[genieconseil]

As a practicing mechanical engineer since 25 yrs in Québec, Canada (same type of climate), the first step is to communicate with the manufacturer and get heat dissapation of the controls, transformer and motor (in BTU) and average operational temperature (30 Celcius is usually a good set point)that is always located in the dedicated mechanical room.
My first question is where is this mec room located?
If it is in a garage area then simplify your design by recirculating the garage air in the mec room with a wall mount evac fan and proportional air intake on the wall of the room, Use 10F as your delta T (where Q=CFM*1.085*delta T) solve for CFM(Flow).
If not possible to do this, then with the BTU (given heat dissapation) size your AC proportionlly. I recommend a standard residential type AC mini split, locate the evaporator in the mec room and if possible locate the condensor in the garage near by (reduce cost of refrigerent lines) in this arrangement the heat is returned in the garage in the winter thus helping heat the garage and in the summer the little heat given in the garage will be taken care of by the garage CO ventilation system (install a thermostat) again if a garage is available! OtherWise the condenser will have to be located outside (make sure you spec a low ambiant kit for the condensor for winter opperation). No need for a heat pump as said in previous post no good payback as you rarely or never need to heat unless your mec room is on the roof and all face of its envelope is exposed to the outside then add a baseboard for security factor. Check your réfrigèrent lines as the have a max. dist they can travel in terms of lift and equivalent lenght (when dist is an issue spec an inverter).

Hope this helps, that is the way it is done here with great success.

Genieconseil

 

[urgross]

Depending on what code you follow, I would recommend a ducted system, unless outside air and postivie pressurization are already available. Does the elevator mechanical room already comply with IBC 3006 and ASME A17.1, and under the local jurisdiction with IMC 403 be applicable? Also, with a ducted system outside air could be used for cooling, as long as RH is controlled.

 

[EnergyProfessional]

geniecounsil: Not sure about code in Canada, but in the US garage exhaust is considered "exhaust" that can't be recirculated in other spaces.
a mechanic may have to work in that elevator room - they usually don't like CO etc.

 

[cdxx139]

Start with the elevator motor HP given by the elevator consultant. Convert to KW then BTU, divide by motor efficiency, then multiply by motor duty factor. And add any solar loads if applicable.

Motor duty factor has always been a number that I have struggled to be comfortable with. trashcanman states 50%.

When possible, I try and design a ducted FCU system located outside the elevator machine room for easier maintenance access. I just duct to the room boundary with a fire dmaper. I have never ducted into an elevator machine rooms for even distribution. Usually not enough space, and the room is so small, it is not typically needed, plus it has a wide temperature range requirement, usally 60 degF to 90.

My state code has a maximum but also a minimum room temp so heat will most likely be required. You should have a problem finding a heat pump with capacity down to 0 degF OA.



knowledge is power

 

[cry22]

this is what we do her in the mid-atlantic:
1. split system AC. Floor mounted FCU indoor if you have the space. no condensate piping over electric equipment.
2. Electric heat, you do need it in case your heat pump fails, you wet-pipe sprinkler pipe could freeze. Since you need some sort of stand-by heat, P does not make sense.
3. Use a wall mounted exhaust fan, maintain room temp with EF when OA temp is 80F or below. Use AC when above adj. of course) AND you get stand-by for your AC system along with an air side economizer.
As for the size, a 10,000 lbs elevator machine room is no more than 30HP motor, no more that 3-ton of heat. Keep in mind you only need to maintain 90F in the room. being on the 18th floor, even in the summer, it is cold up there, your EF by itself will do the job.