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Circulating air between floors

I don't see a lot of air mixing between floors in my (partly finished) house. We had a hot day here yesterday (34C / 93F), and by sunset the first floor was 22C / 72F while the upstairs was around 24.5C / 76F. This doesn't surprise me, as hot air obviously rises, plus the 1st floor has the benefit of the slab heat sink. What surprised me is that this morning the temperatures were the same. I would have thought with minimal heating going on during the night, they would have equalized at least somewhat. (There was no cooling last night, it never went below 24C and I woke up at 6:45 to a temperature of 27C).

We have a wide, straight stairway in the centre of the house. Would it be worthwhile to put a duct between two communal areas of the two floors and a duct fan? Or would this be a lot of work for minimal benefit?

Note: we don't have the HRV running yet, but my understanding is that wouldn't mix enough air to make a lot of difference.

Asked by Trevor Lambert
Posted Jun 18, 2018 8:56 AM ET
Edited Jun 18, 2018 9:44 AM ET

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6 Answers

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1.

Trevor,
Does your house have air conditioning?

If so, is it a ducted system or a ductless system?

If you are trying to cool two floors with a single ductless unit on the first floor, it won't work. You'll need a ductless minisplit upstairs to provide cooling for your second floor.

Answered by Martin Holladay
Posted Jun 18, 2018 9:44 AM ET

2.

No air conditioning. I know there are going to be times when the two floors are different temperatures, but I thought there would be at least some, partial equalization overnight.

Answered by Trevor Lambert
Posted Jun 18, 2018 12:28 PM ET

3.

Trevor,
No, the warm air wants to stay upstairs, and the cool air wants to stay downstairs. I don't think it makes much sense to try to use a duct and a fan to equalize temperatures -- the results won't be good enough to justify the investment and electricity use.

Install a ductless minisplit upstairs if it's too hot up there.

Answered by Martin Holladay
Posted Jun 18, 2018 12:34 PM ET
Edited Jun 18, 2018 12:35 PM ET.

4.

My wife would never approve that proposal. My next idea is to feed the glycol ground loop (used for the HRV in the winter) up to a water-air heat exchanger on the second floor with a box fan attached. How crazy is that? If that's too crazy, I will have to just resign myself to being hot for a couple of weeks a year.

Answered by Trevor Lambert
Posted Jun 18, 2018 12:47 PM ET
Edited Jun 18, 2018 12:47 PM ET.

5.

Trevor,
First of all, your glycol ground loop isn't restricted to winter use. Most owners of HRVs with a glycol ground loop use the loop during the summer as well as the winter. During the summer, the glycol ground loop will lower the temperature of your ventilation system's supply air.

I don't recommend adding an additional heat exchanger to try to get more "coolth" out of your glycol ground loop. If the ground loop was sized properly, it will handle the needs of your HRV. If you run the system more aggressively (through a new heat exchanger), you'll just succeed in heating up the soil around your ground loop, making it less effective in August.

Answered by Martin Holladay
Posted Jun 19, 2018 6:16 AM ET

6.

I know I could use the ground loop in the summer with the HRV. My reason for not doing that is I think they will actually fight each other. Let's say the ground temperature is 10C, the outside air is 27C, indoor air is 24C, desired temp is 21C. If the incoming air at 27C is fed through the ground loop heat exchanger, it will lower it some amount (I don't know what amount, but my one assumption is it will be below the indoor temperature; if not, then my whole premise is out the window). For sake of illustration, let's say the air coming out of the heat exchanger and into the HRV is 18. The HRV will do its job, and transfer heat from the outgoing stream and deliver air at say 23. Pretty close to the same temperature that would have been delivered by the HRV on its own.
To clarify, the other heat exchanger wouldn't be additional, I would switch from one to the other. I wouldn't be running anything more aggressively, I'd just be getting the cooling that the HRV would otherwise be putting back outside.

Perhaps a more reasonable thing to do would be to just move the heat exchanger from the incoming fresh air stream to the outgoing supply air stream in the summer. This was my original idea, before becoming concerned with the temperature differential on the two floors. Much easier, and can be completely undone if it doesn't work as expected. I will put off doing that until next summer, then I will actually have something to compare to.

Answered by Trevor Lambert
Posted Jun 19, 2018 1:14 PM ET

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