How much energy is required to heat up air?

[electricaleng30]

We have 3 large air unit bringing in fresh air from the outside and sort of act as an air exchanger for our manufacturing plant during the summer time. Now in the winter time, we do the same thing, but we try not to bring in as much fresh air (through dampers)in because of the large cost associated with warming up cold -20 degree celcius air. What I am trying to find out is how much energy is required to warm up air 1 degree celcius so we can figure out our energy cost associated with heating up that cold air with gas heaters built in the units? I understand that the size of the duct probably has a lot to do with the matter, but for now, an average would help greatly. I am not sure if I've posted this question in the right forum, but if I've posted this in the wrong forum, could someone please redirect my question to the appropriate one? Thank you very much for your help.

 

[quark]

What you should, first, know is the flowrate of air, if the system is already existing one. Then it is as simple as using the equation Q = 1.08 x cfm x dT (1.1 is better and conservative). Q is heat flowrate in btu/hr, dT is temperature difference in F.

Alternately, in SI, you have the equation Q = 1.2x m³/s x dT, where Q is kW and dT is temperature difference in ⁰C.

 

[STYMIEDPIPER]

quark provided you with determining total kw required. You need to determine your cost per kw.

Earlier issues of the 'Industrial Ventilation Handbook' provides two (2) equations which may help;

Hourly cost = (0.001QN) / q x c
Yearly cost = (0.154QDdg)/ q x c

Q = air volume, cfm
N = required heat, BTU/hr/1000 cfm (table in referenced book
D = operating time, hours/week
q = available heat per unit of fuel
dg = annual degree days (table in referenced book or others)
c = cost of fuel, $/unit

 

[lilliput1]

stymiedpiper you should also divide by the efficiency. Average seasonal efficiency for a gas heater is about 70% so you should divide by 0.7

 

[STYMIEDPIPER]

lilliput1

You are absolutely correct
I usually use 80 %
I had a clint whom insisted that I use 90 % becuse that is what the equipment salesperson told him