# Heat load calculations with heated air changes

I am working on a building project that requires a high ventilation rate for fire safety: 6 air changes per hour (ACH). The winter design temperature is -14, so moving that much air through the system will obviously impact the total building heat load significantly with a 200,000 ft3area.

When I run the analysis with the Revit loads tool before setting the ACH, it returns a heat load of 103,000 Btu/hr. If I set the zone ventilation to 6 ACH, it returns a heat load of 1,662,000 Btu/hr. From a simple heat transfer standpoint, it would make sense that the heating load would skyrocket when you are pumping that much cold air into the building. However, during the winter, part of that makeup air will be infiltrating the building through a heater, so the delta T will not be the difference between the -14 degrees F, and the 50 degree F setpoint, but, rather the heater output temperature and the setpoint.

Does anybody know of a way to account for this within Revit?

• Somebody suggested reducing the ventilation rate by the airflow rate through the heater, but without any calculations that I can't think of how to set up, I feel like there would still be SOME added heat load created by the heaters that needs to be accounted for. Apr 17, 2017 at 15:36
• Sounds like this building would benefit from a recuperator - running the incoming air through a heat exchanger with the outgoing air. Apr 17, 2017 at 15:51
• Do you specify the input air temperature? If so, you could change that to be the temperature of the air after the heater. If you are looking for Revit specific support, you should probably try to find a specialized forum for faster help. Apr 17, 2017 at 17:08
• @BrianDrummond - I was assuming that's what is meant by "heater". It seems to me that if the OP means any other kind of heater, then the calculations are correct as shown, with the heater providing a significant part of the load.
– Mark
Jun 17, 2017 at 12:50
• I'm voting to close this question as off-topic because the need for an answer has long since passed and the revit specific nature of the question is not really a fit for the more general engineering focused nature of this stack. Sep 12, 2019 at 19:24

## 1 Answer

I know it is not what you asked, but you could take the intake air below ground, 2m down for example, and benefit from the ground temperature compared to the ambient air temperature - called a "puit canadien" and i did this for a 4 bedroom house in Switzerland - needed 30m of pipe 2m down plus a heat exchanger as @Brian Drummond . Helps in summer to reduce air T and winter to increase air T. Several references can be found online - just make sure that you have a constant slope and get rid of any moisture...

• I've never heard of a Canadian well... it's very intriguing, though. I'll look into it for other projects; strangely i don't find an American equivalent.... Apr 18, 2017 at 2:14
• Possible examples : zehnderamerica.com/products/geothermal-heat-exchangers or ceresgs.com/… Apr 18, 2017 at 4:41
• Thanks for the examples. We don't really have room for anything like that on this project, but it may come in handy down the road. Apr 25, 2017 at 2:02
• Revisiting this quite awhile later, this was a good idea. I didn't use it here, but have used it since. Sep 12, 2019 at 19:20
• @Secundus glad it helped, cheers. Sep 12, 2019 at 19:30