Balanced Pressure Ventilation with Heat Exchanger worth it?

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#3082521 30-May-2023 18:33

Ten years ago, I visited a local ventilation installation company and got a five minute run down on what was important. I Also had prices for balanced heat recovery. The heat exchangers were $3,000-$5,000. That was too much for a 1960 house which leaks air so we moved to other cheaper technology like more insulation, heat pumps and dehumidifiers.

This related topic I remembered from 2014:
Positive Pressure or Balanced Pressure ventilation system?

There was at least one more topic that was on similar options but got into the heat losses from ducting in a lot more detail - I’ll look for it when I have time.

Handle9

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#3082522 30-May-2023 18:34

photon:

If air temperature inside is 20 degrees and air outside is let's say 4 (coldish average in Christchurch during nights), then after the heat exchanger, the coming air would be (20 - 4) / 2 = 12. Taking into account the exchanger is only 80% efficient on maximum, it would be 12 * 0.8 = 9.6 at best. Taking into account heat loss in 20 meters of ducting (R0.6-0.8 insulated), I heard 1 degree loss for each 3 meters on average, it could be well close to 6-7 degrees. At this incoming temperature, it looks like the BPS should be turned off too or face higher power bills for heat pumps, as it is only 2-3 degrees higher than what I would get with PPS, but 3.5K more expensive. If I am correct above (?) it means the heat exchanger does not actually make a big difference in usability comparing with choices 1 or 2 with PPS. And so, I should be getting down the road to spend 1700NZD for way more powerful PPS and ventilate more intensively during a day and have an option to switch over automatically from/to outside/roof cavity. Is there anything I am missing?

Your calculations are flawed, you are trying to approximate delta T for energy exchange.

It's a heat exchanger, it's 80% efficient for energy not temperature. Even at zero degrees C air has significant energy in it, which is why heat pumps still work below the zero degrees. Humidity also plays a big role in this calculation.

I'm not able to do the calculations but it's not just a delta T calculation.

Handle9

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#3082524 30-May-2023 18:37

This is an example from the Mitusbishi Electric technical manual showing how the calculations work

https://www.mitsubishi-les.info/database/servicemanual/files/TM_LGH_RX5_GB_Jan_2010.pdf

edit: Included the full page (U-23)

zenourn

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#3082568 30-May-2023 20:33

I had a balanced pressure ventilation with heat exchanger system installed last year (4 extraction vents, 6 supply vents). I quite like it, made a big difference in CO2 levels, keeps the air fresh, and greatly reduced condensation.

Have just done some temp measures (using a Fluke 87V):

Outside air temp: 10.3'C
Average temp by extraction vents: 19.5'C
Average temp of air being supplied into rooms (measured just inside vent): 17.1'C

That seems quite reasonable to me.

Here in the middle of winter can get -7'C outside and 26'C inside (with fire) so can repeat with larger deltas.

tweake

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#3082579 30-May-2023 21:12

Handle9:

This is an example from the Mitusbishi Electric technical manual showing how the calculations work

https://www.mitsubishi-les.info/database/servicemanual/files/TM_LGH_RX5_GB_Jan_2010.pdf

edit: Included the full page (U-23)

thank you for that, its very handy.

of interest is that its a commercial unit, but if you scale down it down (assuming efficiencies stay about the same) the ventilation load on a 100sqm house in those conditions (at 0.5 ach) is roughly, erv 400 watts hrv 700 watts and pps 1.4kw. tho a pps would typically not be running in those conditions and you would not get any forced ventilation.

actually those conditions are similar to auckland on a frosty night.

tweake

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#3082581 30-May-2023 21:17

timmmay:
tweake: . i still get given a hard time for being "extravagant" because i have 3 heat pumps.

Haha, I have three including one ducted unit. It wasn't practical to duct the whole house for a variety of reasons.

nice.

its just people expect you to be rugged up, wearing outdoor clothes, sitting in a cold house, freezing cold bed, all to save $40/month in heating for a the few months of winter.

MikeAqua

7779 posts

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#3082671 31-May-2023 10:17

We put a BPS system, in a 1950s house in Nelson. We went with SmartVent, based on friends' experience.

The difference to the house was phenomenal. The SmartVent guy (I dont' recall his name) made no overt efforts to sell. He just clearly knew his stuff. He set up the system so that on balance it moved air from the sunniest rooms in the house toward the cooler rooms. This spread an even background heat throughout the house, including warming up furniture.

The air, furniture etc felt noticeably drier. We were able to run the heat pumps a few degrees drier for the same comfort level. I'm not sure if this was because the air was drier and/or because the furniture was warmer.

He also upgraded our bathroom extraction. No more condensation on the mirror, when the shower was running. In fact, very little condensation anywhere. On cool nights there would be a little condensation in the corners of single glazed bedroom windows not even on single glazed windows.

When we moved, into a sunnier, warmer double glazed well insulated house, it was noticeably damper. So, we got the SmartVent guy back. He took one look at our house (two level) and said a smart vent system couldn't be installed in a wat that would work well.

He recommended (and installed) a fan above the central stairwell atrium to push warm air down during the day in winter and suck cool air up during the day in summer. Worked well.

Mike

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Shop now on Samsung phones, tablets, TVs and more (affiliate link).

rb99

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#3082765 31-May-2023 13:29

timmmay:

3puttssuck:

Which WindowVac to you use mate?

A Karcher Window Vac my wife got from Mitre 10. Not sure which model but looking at the website looks like a WV2 (link). I think any would work fine.

btw, should anyone be interested...

Bunnings -

https://www.bunnings.co.nz/karcher-wv-6-plus-window-vac_p0129279

Mitre10 -

https://www.mitre10.co.nz/shop/karcher-window-vac-wv6-plus/p/337644

so 15% off at Mitre10 = $149.60 (I think)

“The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness.” -John Kenneth Galbraith

rb99

Paul1977

5042 posts

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#3082801 31-May-2023 14:55

photon:

I am more worried about getting continuously fresh air in for better health and better sleep. And here is the biggest puzzle among 3 choices:

1. stop PPS or slow it down significantly during colder nights (<6 degrees), which might be OK as the fresh air would be brought during a day multiple times anyway
2. do not stop PPS but have heatpumps going full on, which might be not ok as the powerful fan can replace the entire air in the house in 30 minutes
3. get BBS with heat exchanger and keep it running during colder nights...

That would be replacing the air too quickly. I believe the recommendation is 0.35-0.5 air changes per hour. So you want it to take 2-3 hours to do a an air change, not 30 minutes.

photon

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Wannabe Geek

#3082915 31-May-2023 16:32

Thanks everyone. The information provided is very useful.

tweake

2391 posts

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#3082955 31-May-2023 18:38

Paul1977:

photon:

I am more worried about getting continuously fresh air in for better health and better sleep. And here is the biggest puzzle among 3 choices:

1. stop PPS or slow it down significantly during colder nights (<6 degrees), which might be OK as the fresh air would be brought during a day multiple times anyway
2. do not stop PPS but have heatpumps going full on, which might be not ok as the powerful fan can replace the entire air in the house in 30 minutes
3. get BBS with heat exchanger and keep it running during colder nights...

That would be replacing the air too quickly. I believe the recommendation is 0.35-0.5 air changes per hour. So you want it to take 2-3 hours to do a an air change, not 30 minutes.

i can't quite remember if the requirement here is 0.3 or 0.35 ach. 0.5 is often what people do when they have balanced systems.

tweake

2391 posts

Uber Geek

#3082957 31-May-2023 18:46

MikeAqua:

The air, furniture etc felt noticeably drier. We were able to run the heat pumps a few degrees drier for the same comfort level. I'm not sure if this was because the air was drier and/or because the furniture was warmer.

He also upgraded our bathroom extraction. No more condensation on the mirror, when the shower was running. In fact, very little condensation anywhere. On cool nights there would be a little condensation in the corners of single glazed bedroom windows not even on single glazed windows.

the bathroom might have plumbed up into the system. thats a pretty common setup and you get constant air flow through the bathroom which keeps it dry.

humidity level is a big factor in comfort. so if the humidity is right you often can be comfortable hotter or colder. that way it can save power. this one of the reasons people are going to whole home dehumidifier and why many in cold dry climates use humidifiers.

however with balanced systems they keep moisture in the home (as well as out of the home). so you need to have a means of drying the home when required or at least some gauges so you can see what the humidity level is, so you can keep it out of the danger zone.

MikeAqua

7779 posts

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#3083258 1-Jun-2023 13:33

tweake:

the bathroom might have plumbed up into the system. thats a pretty common setup and you get constant air flow through the bathroom which keeps it dry.

humidity level is a big factor in comfort. so if the humidity is right you often can be comfortable hotter or colder. that way it can save power. this one of the reasons people are going to whole home dehumidifier and why many in cold dry climates use humidifiers.

however with balanced systems they keep moisture in the home (as well as out of the home). so you need to have a means of drying the home when required or at least some gauges so you can see what the humidity level is, so you can keep it out of the danger zone.

The bathroom was still a separate system with a separate fan, activated from the same switch.

Mr Smartvent increased the diameter (inlet, outlet, duct and fan) and put in a more powerful fan. Simply moving more air than the old system.

I'm not following you on how balanced systems keep moisture in the home?

Mike

tweake

2391 posts

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#3083347 1-Jun-2023 15:25

MikeAqua:

tweake:

the bathroom might have plumbed up into the system. thats a pretty common setup and you get constant air flow through the bathroom which keeps it dry.

humidity level is a big factor in comfort. so if the humidity is right you often can be comfortable hotter or colder. that way it can save power. this one of the reasons people are going to whole home dehumidifier and why many in cold dry climates use humidifiers.

however with balanced systems they keep moisture in the home (as well as out of the home). so you need to have a means of drying the home when required or at least some gauges so you can see what the humidity level is, so you can keep it out of the danger zone.

The bathroom was still a separate system with a separate fan, activated from the same switch.

Mr Smartvent increased the diameter (inlet, outlet, duct and fan) and put in a more powerful fan. Simply moving more air than the old system.

I'm not following you on how balanced systems keep moisture in the home?

a tad odd to have a separate bath system, unless it could not be plumbed into the other system. or they just wanted to sell more stuff.

one of the problems doing a separate system is that you need make up air, especially if the fan is upgraded. some ventilation systems have that option and will boost incoming airflow when the bath fan gets turned on (or stove hood). but generally its cheaper and gets better results, to just use the bath room as one of the ventilation exhausts.

sorry i may have gotten my wires crossed here. depends on if you have HRV core or ERV core. HRV keeps inside heat in and outside heat out. ERV keeps inside heat and humidity in and outdoor heat and humidity out. the downside of the ERV is because it keeps that moisture in, it can build up to danger levels. this is also why its important to know what core they sold/installed.

MikeAqua

7779 posts

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#3083804 2-Jun-2023 12:22

tweake:

a tad odd to have a separate bath system, unless it could not be plumbed into the other system. or they just wanted to sell more stuff.

one of the problems doing a separate system is that you need make up air, especially if the fan is upgraded. some ventilation systems have that option and will boost incoming airflow when the bath fan gets turned on (or stove hood). but generally its cheaper and gets better results, to just use the bath room as one of the ventilation exhausts.

sorry i may have gotten my wires crossed here. depends on if you have HRV core or ERV core. HRV keeps inside heat in and outside heat out. ERV keeps inside heat and humidity in and outdoor heat and humidity out. the downside of the ERV is because it keeps that moisture in, it can build up to danger levels. this is also why its important to know what core they sold/installed.

I wanted the bathroom system set up that way. Simpler. The house was a 1950s and 1970s build so not air-tight and easy to draw make-up air.

The core was an air-to-air heat exchanger. Cold dry air sucked in and warm wet are sucked out with transfer of most heat from outgoing to incoming air. Worked well enough to justify the investment. Humidity would stabilise at ambient or below if we were running heat pumps in cooling mode.

Mike

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