Modeled air sealing in zone 3. Energy use increased
big__o
| Posted in General Questions on
What am I doing wrong. I was having a discussion with someone that in my zone 3a air sealing doesn’t save much money.
So,using energy plus via beopt, I modeled a below code minimum house- Dallas tx, 1800sf, 7ach50 , no ventilation, and then the exact same house but with passive house tightness of 0.6ach and a 70% erv, no dehumidifier – total energy use actually increased with the air sealed house and it showed higher humidity in the summer.
Could this be possible?
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I'm not super familiar with beopt, but if I had to guess, it might be because "no ventilation" is of course more energy efficient than an HRV! It just is problematic from an interior air quality point of view ;)
Is there a "natural ventilation" or "exhaust only ventilation" option you could use for your base case? This would either represent occupants opening windows or using bath fans to get fresh air in the base case.
good point. I added exhaust ventilation and that changed the output a bit. although with 7ach I dont know if any additional ventilation would be a good idea.
here are the outputs from best to worst
passive house level air seal with no ERV(probably not wise) :11,518 KW/year
below code minimum house with no ventilation: 12,183 kw/year
passive house level air seal with .70 erv: 12,456 kw/year
below code minimum house with exhaust only ventilation: 12,535 kw/year
I dont doubt that air sealing with mechanical ventilation may provide superior air quality. Ive been looking for research but havent found any. Do you perchance have links to any?
When I said no ventilation was problematic I was trying to make a joke (always a bad idea!)--I meant that what you were modelling when you picked "no ventilation" may have been a house with no bath fans, no range hood, and no operable windows. I don't think you need research to understand why that wouldn't be a comfortable place to live! But that's not a real option you are considering, it just may have been what you modeled on accident (again, I'm not super familiar with BeOpt).
As far as what you're actually trying to compare: typical exhaust-only ventilation in a leaky house vs balanced ventilation in a tight house with an ERV or HRV, I'm not shocked that in your climate the energy differences aren't huge.
I don't know much about ventilation in humid climates, but you may find something useful in this article: https://www.greenbuildingadvisor.com/article/6-ways-to-ventilate-homes-in-humid-climates
Actually I don't have bathroom exhaust in my current house. Hasnt been a problem. Per the model, a 7ach50 house at it's least is exchanging 35cfm with the outside and at worst over 100cfm iirc. I do have a range hood though but it is not on all the time. Selecting exhaust only on beopt assumes it runs all the time so I think selecting no ventilation would be closer to how most houses in this zone are operated
Sound right to my ear.
Seems to me EVRs much south of Canada are silly. Note when the delt T is less than 20° almost no energy gets transferred. My guess 70% of the hours you have a delt T close to 30°.
If your bit of TX is as muggy as the parts I have visited any ventilator will bring in tons of moisture that will be expensive to remove.
My opinion is EVR/HRVs are over hyped in most climates and yours in particular. Yes, someone will come along and tell us how you will suffer brain damage without one in the leakiest of houses but I say the damage is preexisting if the occupants fail to notice the air in the house is stuffy and crack open a window.
Try running BEopt without the ERV.
Walta
thanks for the reply. I did look at the indoor humidity and the air sealed house with erv was more humid but only marginally so. the regular house peaked at around 64% rh in summer, while the air sealed house peaked around 66%
I also looked at Chicago and in that zone the below code minimum house lost to the air sealed house- but not by a lot . 18,007 kw/y for the below code house and 17,679 kw/y for the air sealed house
Btw, I didn't know about the lack of great transfer when Delta t is less than 20 f. Good to know. Thanks!
the air sealed house with no ERV had the best results but I wouldnt want to live in such a house.
here is the data
passive house level air seal with no ERV(probably not wise) :11,518 KW/year
below code minimum house with no ventilation: 12,183 kw/year
passive house level air seal with .70 erv: 12,456 kw/year
below code minimum house with exhaust only ventilation: 12,535 kw/year