air CFM to BTU

Hi

We have heated air we want to reuse to heat the working areas in our building.

I have the temperature and flow (in CFM) of the air comming out of the exhaust. In average, it is 45oC at about 1 000 CFM and we have 4 of those exhaust.

I want to know the BTUs (or ton of air, since 1 ton of air = 12 000BTUs) available so we can maintain a confortable ambiant temperature in the building, or if I can make it this way: what heating capacity do we have from the exhaust?

I try to figured it out myself, but got lost with the unit conversion since they always talk abour ton of cooling air and I want to heat.

Thank you very much to whoever will help me.

[Robert Fogt]

I cant help you. But I found a site that probably can.

http://www.ajmadison.com/phpdocs/ajt...ying_guide.php

I think your best bet would be to email them and ask your question.

If they are able to answer you could post their reply here, as it may benefit others. If they cant answer, let me know and I will continue searching.

Hi Marc - did you ever get an answer to your question - I have a similar question - thanks Terry

Just incase someone else needs this info.

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CFM * 1.08 * tRise = Btu/hr
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General information follows.

That factor is based on standard conditions which are at sea level and A standard humidity level which i do not remember off hand. As altitude increases the factor decreases. At 2100 feet it is roughly 1.0.
The humidity also affects this number. Generally the greater the humidity the greater the factor.

1.08 Will be good enough for most applications though.

I'll give an example of the use:

Suppose the room temperature is 65.
We have a 1200 CFM blower. We measure an output temperature of 100.
100 - 65 = 35 tRise.

Now we have all the numbers to get our BUT/hr.

1200 * 1.08 * 35 = 45,360 btu/hr


This particular problem often compilments another, And that is how do we verify the CFM is as cited or measured with an anemometer.

Assuming we have electric heat and the temperature probe is not in line of site of the heating elements (to be sure we are not measuring the IR radiation) All you need to know is the power consumption. Either measure it with an amp meter. Or go with cited figure(not as accurate).


CFM = btu / (1.08 * tRise)


For reference: 1 kw/hr = 3412.14 btu


assume we have a 15kw heater and a tRise of 22

15kw * 3412.14 = 51182.12 btu

now we can solve for CFM

51182.12 / (1.08 * 22) = 2154.

In that example our result is 2,154 CFM.

If that conflicts with a suspected figure An investigation is required.

Keep in mind the factor is based on standard conditions. As a rule of thumb the result should be within 10% of the calculation. Anything out of this range is a trouble spot. Most likely to be a dirty air filter, or incorrect power factoring.

Hope this helps.

Thank you this info was very much usefull

[QUOTE=Marc]Hi

I am trying to figure out what cfm hood is needed for a gas cooktop that when all burners are going will burn 15,000 btu per hour.

I have a HVAC unit that delivers 10,200 cfm heating / cooling to an area. Is there a simple way to come up with a cost per hour to run this. We pay .09cents per kw. I know that there is 5.5cfms per kw will that give me a close enough calulation if we to rent this area out and charge by the hour.

The general equation to answer your question is like this: BTU = cfm * 1.08 * (Tin - Tout)

how many cfm is needed to vent 230,230 btuh from a bakery?
Ed Swaby [contact info removed]

welll you get from 400 to 450 cfms from 12000 btus