HVAC Running Cost

[DoggyDog]

Hi all,

I'm new to this site...please be gentle!

Is there a "rule of thumb" for air conditioning operating cost based on the amount of cooling required? I'm trying to evaluate how much it will cost (for electricity) to operate an A/C to cool 60kW of heat in a sealed room.

Any help is greatly appreciated.

 

[MintJulep]

In short, no, at least not without more info.

The performance indicator you are interested in is Coefficient of Performance (COP). For a cooling application, COP = cooling effect / power input to operate the system.

Manufacturers will probably list COP in the technical data for the system. However, what is listed is at some set of conditions (combination of evaporating temperature, condensing temperature and load). These conditions should be stated (but frequently are not), and will probably be different from your condtions. COP is not constant, it is a function of both evaporating and condensing temperature.

 

[lilliput1]

$/yr = 1.2 Kw/Ton x $/Kw x tons x 1600 full load hours/yr


1.2 kw/ ton if air cooled. Say 0.8 Kw/Ton for water cooled, including chilled water pump & condenser water pump.

Full load hours depend on location & occupancy type. It could be as high as 2000 & as low as 1200.

 

[DoggyDog]

Thanks for the reply...I'm going to show my age and ignorance by asking what is a Ton? I live in the metric world...

 

[sathanasiou]

You could calculate the cost using this:

(cost of electricity)*(consumption)*(hours of operation/day)*(days of operation/year)=cost for one year

Note that power consumption is usually different in cooling and heating modes, so do the calculations for both and add them up.

If you divide the cost by the capacity of the A/C unit, you will get an estimation for the cost/kW.

Remember that one Ton = 3.52 kW. For all unit conversions, try downloading "Convert" from:

http://www.joshmadison.com/software/convert/

Hope this is useful!

 

[MintJulep]

At ton of refrigeration is the energy required to change 1 ton (2000 pounds) of water at 32 F to ice in one day.

Equal to 12,000 BTU/hr or 3.52 kW.

 

[racingdan]

60 kW * 3.413 BTUh= 204,780 BTUh
_ MUCHO Tons ... in the 25-Ton range.

Considering equipment S.H.R. and average efficiency,
= $60 per day or $21,900 per year
( ~$2.50 /hour based on $0.10/kW)

Just use a 7000 CFM Exhaust fan,
to limit area temp increase to ~ 25'F
__ ~105'F when it's ~ 80'F outside or
__ ~ 65'F when it's ~ 40'F outside.

Assuming 60kW heat is from a process
(i.e. heater, furnace)

NOTE: One-Ton equipment does NOT take 3+ kW to operate.
Power requirement is likely close to 1.0 kW/Ton
depending on system type ( DX or chiller)
and actual overall efficiency.