Balanced Pressure Ventilation with Heat Exchanger worth it?

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photon

5 posts

Wannabe Geek

#304712 30-May-2023 00:39

I have asked 20 different companies for quotes for Positive Pressure Ventilation and Balanced Pressure Ventilation with Heat Exchanger. It turned out this topic is very much heated in NZ. My findings are:
- PPS sales people tell that heat exchanger is not efficient for the money asked.
- BPS sales people tell that the PPS is not good because it pushes out all the heat from a house causing higher power bills.
- Sales people who sell both systems let me to choose saying BPS is better and so more expensive so it is for me to choose what suits my budget.

It is all great but unhelpful. So, I am posting it here with hope you could help me to review my thinking and confirm who is right who is wrong.

I have found that:

If I consider only manual controllers, I save about 1000NZD for any type of system. And I actually need only manually controlled systems as these will be connected to home automation anyway and be controller by my automation depending on temperatures, humidity and weather forecasts.
If I DIY, it will save me 1000-1500 on average, which is great, it is only 4-6 hours job really.

Price wise:

The cheapest but least powerful (500m3/h) PPS would cost me about 2000NZD (DIY) for 6 outlets. And 1600NZD (DIY) if I source great power fan (1200m3/h) from hvac company directly and ducts and components separately (i.e. not as a complete kit, but I would need to know exactly what I need, which I know now). PPS would be able to source the air from outside or from the roof cavity, again controlled programmatically by my automation. Yes, I know the air from roof cavity is dusty, but I checked it is actually warmer on average (so can ventilate more intensively or use that heat, although I know it would be only marginal) and with F8 grade filter dust is a solved problem. PPS would push the air through the bathrooms and kitchen exhaust pipes, which are always open, but vented when bathrooms or kitchen are used.
The cheapest and the least powerful BPS with a heat exchanger would be around 4500NZD, but only good enough for 5 outlets, not 6 as per my requirements. 6 outlets is 5400. BPS at this price would only source the air from outside.

So, I would say 3000-3500NZD price difference on average.

Problem solving wise:

Both system will solve moisture no worries. My home is modern and relatively dry but colder days cause condensation of window frames.
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...

The 1 and 2 are more or less clear. Now about the 3. 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?

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#3081248 30-May-2023 08:38

Balanced is clearly better, bringing in fresh air warmed by the heat of the expelled air. The main question I think is is it worth the extra cost?

You will never eliminate condensation on windows and frames entirely, there's always going to be a temperature differential and moisture in the air. I use an electric window vac to remove water from the windows that collects there on particularly cold days, but we get no condensation on the PVC frames.

I don't think you need fresh air continuously, though with a balanced system it wouldn't hurt much to have it running, but slowly when it's cold outside.

I have an old house with a positive pressure system, which is plugged into a WiFi controlled plug, no controller at all, but connected to Home Assistant to schedule it. I run it for:

Two hours around the middle of the day to bring in fresh air and remove moisture
For an hour after we've been cooking to get rid of smells
If the temperature and humidity is ok it turns on for 15 minutes a couple of other times per day - more in the summer

This works well. The output diffuser is beside the input to the ducted heating system, so I use the ducted system on fan to push fresh air around the house. I also close the bedroom doors and crack the windows open when it's running sometimes to push stale air outside.

3puttssuck

744 posts

Ultimate Geek

#3081251 30-May-2023 08:46

timmmay:

Balanced is clearly better, bringing in fresh air warmed by the heat of the expelled air. The main question I think is is it worth the extra cost?

You will never eliminate condensation on windows and frames entirely, there's always going to be a temperature differential and moisture in the air. I use an electric window vac to remove water from the windows that collects there on particularly cold days, but we get no condensation on the PVC frames.

I don't think you need fresh air continuously, though with a balanced system it wouldn't hurt much to have it running, but slowly when it's cold outside.

I have an old house with a positive pressure system, which is plugged into a WiFi controlled plug, no controller at all, but connected to Home Assistant to schedule it. I run it for:

Two hours around the middle of the day to bring in fresh air and remove moisture
For an hour after we've been cooking to get rid of smells
If the temperature and humidity is ok it turns on for 15 minutes a couple of other times per day - more in the summer
This works well. The output diffuser is beside the input to the ducted heating system, so I use the ducted system on fan to push fresh air around the house. I also close the bedroom doors and crack the windows open when it's running sometimes to push stale air outside.

Which WindowVac to you use mate?

timmmay

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#3081254 30-May-2023 08:51

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.

photon

5 posts

Wannabe Geek

#3082304 30-May-2023 11:23

timmmay:

Balanced is clearly better, bringing in fresh air warmed by the heat of the expelled air. The main question I think is is it worth the extra cost?

You will never eliminate condensation on windows and frames entirely, there's always going to be a temperature differential and moisture in the air. I use an electric window vac to remove water from the windows that collects there on particularly cold days, but we get no condensation on the PVC frames.

I don't think you need fresh air continuously, though with a balanced system it wouldn't hurt much to have it running, but slowly when it's cold outside.

I have an old house with a positive pressure system, which is plugged into a WiFi controlled plug, no controller at all, but connected to Home Assistant to schedule it. I run it for:

Two hours around the middle of the day to bring in fresh air and remove moisture
For an hour after we've been cooking to get rid of smells
If the temperature and humidity is ok it turns on for 15 minutes a couple of other times per day - more in the summer
This works well. The output diffuser is beside the input to the ducted heating system, so I use the ducted system on fan to push fresh air around the house. I also close the bedroom doors and crack the windows open when it's running sometimes to push stale air outside.

It is not actually "clearly better". If it is 4 degrees outside and 20 inside, the "heated" air coming to the house is only about 7 degrees. So, it is a tiny bit better, but not clearly. Unless I messed up calculation somehow in the original post?

timmmay

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#3082315 30-May-2023 11:45

It's going to be better as the air coming in is pre-warmed to some extent, the question is how much better.

I'm not sure your calculations are accurate, I can't do any better, hopefully someone else can. With 20c air outgoing and 4c air incoming the air is likely to be around 17 degrees if the heat exchanger is 80% efficient. There will be some heat loss from the insulated ducting, but 1 degree per three meters sounds a bit high, but that's not an expert opinion. Use the R1.0 insulated ducting to minimise heat loss. 20m of ducting isn't unreasonable, but instead of running ducting direct to each room for distant rooms you could run a larger duct and split it further up.

Suggest you try to find a formula for heat loss through insulated ducting. If it's 4 degrees in the ceiling cavity and 17 degrees in the ducting that's not a huge difference, a ducted heating system would have 50 - 60 degree air in the ducting so the loss would be much greater.

tweake

2391 posts

Uber Geek

#3082401 30-May-2023 13:53

photon:

I have asked 20 different companies for quotes for Positive Pressure Ventilation and Balanced Pressure Ventilation with Heat Exchanger. It turned out this topic is very much heated in NZ. My findings are:
- PPS sales people tell that heat exchanger is not efficient for the money asked.
- BPS sales people tell that the PPS is not good because it pushes out all the heat from a house causing higher power bills.
- Sales people who sell both systems let me to choose saying BPS is better and so more expensive so it is for me to choose what suits my budget.

It is all great but unhelpful. So, I am posting it here with hope you could help me to review my thinking and confirm who is right who is wrong.

I have found that:

If I consider only manual controllers, I save about 1000NZD for any type of system. And I actually need only manually controlled systems as these will be connected to home automation anyway and be controller by my automation depending on temperatures, humidity and weather forecasts.
If I DIY, it will save me 1000-1500 on average, which is great, it is only 4-6 hours job really.
Price wise:

The cheapest but least powerful (500m3/h) PPS would cost me about 2000NZD (DIY) for 6 outlets. And 1600NZD (DIY) if I source great power fan (1200m3/h) from hvac company directly and ducts and components separately (i.e. not as a complete kit, but I would need to know exactly what I need, which I know now). PPS would be able to source the air from outside or from the roof cavity, again controlled programmatically by my automation. Yes, I know the air from roof cavity is dusty, but I checked it is actually warmer on average (so can ventilate more intensively or use that heat, although I know it would be only marginal) and with F8 grade filter dust is a solved problem. PPS would push the air through the bathrooms and kitchen exhaust pipes, which are always open, but vented when bathrooms or kitchen are used.
The cheapest and the least powerful BPS with a heat exchanger would be around 4500NZD, but only good enough for 5 outlets, not 6 as per my requirements. 6 outlets is 5400. BPS at this price would only source the air from outside.
So, I would say 3000-3500NZD price difference on average.

Problem solving wise:

Both system will solve moisture no worries. My home is modern and relatively dry but colder days cause condensation of window frames.
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...
The 1 and 2 are more or less clear. Now about the 3. 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?

ok, this is a big topic so i'll try to keep it simple.

condensation on window frames is not a ventilation issue, its a crappy low nz standard windows issues. i think this month that changes for those building new.

PPS vers balanced, all depends on how air tight the house is. typically its not really worth doing balanced ventilation until the house air leakage is below 5 ach50. otherwise you have as much ventilation going through the walls as you do through the ventilation machine. at that air leakage or higher go PPS.

the big advantage with balanced is its constant ventilation, they do not slow down for temps etc. also many people increase the ventilation rate more than the minimum required. which is a good thing as thats healthier, which i doubt the sales people mentioned. however the big question is HRV vers ERV. HRV keeps heat in/out, ERV keeps heat and moisture in/out. ERV is generally better but really requires a dehumidifier to control the house humidity level. also balanced has exhaust inlets which you can do a few tricks like install them in the bathroom and not have a bath fan, not recommended for kitchens however.

with PPS i recommend auto inlet change over so you can use ceiling air or outdoor air. most systems shut off when to hot, so switching to colder outside air keeps the ventilation going longer. a simple thermostat works just fine.

andrew75

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#3082402 30-May-2023 13:56

I had a DVS reclaim unit in my last house.
I am extremely dubious about the benefit of the
heat exchanger. I suspect it was all
snake oil. Ask the company to supply hard
data showing the effectiveness of their unit -
i.e. real world measures of temps of the air going in and out.

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photon

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Wannabe Geek

#3082414 30-May-2023 14:36

timmmay:

It's going to be better as the air coming in is pre-warmed to some extent, the question is how much better.

I'm not sure your calculations are accurate, I can't do any better, hopefully someone else can. With 20c air outgoing and 4c air incoming the air is likely to be around 17 degrees if the heat exchanger is 80% efficient. There will be some heat loss from the insulated ducting, but 1 degree per three meters sounds a bit high, but that's not an expert opinion. Use the R1.0 insulated ducting to minimise heat loss. 20m of ducting isn't unreasonable, but instead of running ducting direct to each room for distant rooms you could run a larger duct and split it further up.

Suggest you try to find a formula for heat loss through insulated ducting. If it's 4 degrees in the ceiling cavity and 17 degrees in the ducting that's not a huge difference, a ducted heating system would have 50 - 60 degree air in the ducting so the loss would be much greater.

If the incoming air is 4 and outgoing is 20 and assuming equal volume goes in and out (i.e. 100% balanced), then at 100% heat exchange efficiency these two streams can do at best is to level each other to the same temperature, which would be 12 degrees. With 80% efficiency the exhaust will be warmer (~14-15) than the the incoming air (~9-10). I do not see how the incoming air can become warmer than the exhaust, physics would not allow it unless there is a powered mechanism to extract heat from the outgoing with some sort of phased coils, but it is not a thing in cross flow heat exchangers.

timmmay

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#3082420 30-May-2023 14:50

photon:

If the incoming air is 4 and outgoing is 20 and assuming equal volume goes in and out (i.e. 100% balanced), then at 100% heat exchange efficiency these two streams can do at best is to level each other to the same temperature, which would be 12 degrees. With 80% efficiency the exhaust will be warmer (~14-15) than the the incoming air (~9-10). I do not see how the incoming air can become warmer than the exhaust, physics would not allow it unless there is a powered mechanism to extract heat from the outgoing with some sort of phased coils, but it is not a thing in cross flow heat exchangers.

Someone explained it to me on a thread here a few years back, with a diagram and all, but I don't recall it well enough to pass it on and I can't find the thread after a quick search. I don't think your understanding is accurate. There will be an article somewhere on the internet about how they work.

tweake

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#3082421 30-May-2023 14:52

andrew75: I had a DVS reclaim unit in my last house.
I am extremely dubious about the benefit of the
heat exchanger. I suspect it was all
snake oil. Ask the company to supply hard
data showing the effectiveness of their unit -
i.e. real world measures of temps of the air going in and out.

i highly doubt the unit is snake oil. typically its another brands unit they rebadge. unless its a complete garbage brand or fake core, it should work fine.

however what kiwis tend to forget is air doesn't hold a lot of heat. most of the cost of heating is heating up the mass of the house. when you look at the $$$ you save, its not a lot per year. its not like the heating bill is cut in half. i doubt many people could even tell the difference as its so hard to measure. the benefits is more about getting more ventilation without increasing cost and resulting in a healthier home. many users will double the ventilation flow rate. also keep in mind this all works hand in hand with everything else in the home. so typically they have much better insulation and of course less air leakage.

having it set up properly is a different ball game.

edit: i forgot a big issue is ducting loses. have ducts outside the house (ie in ceiling) makes it less efficient and duct leakage makes it worse. its far better when ductwork in in the conditioned space. also the house really needs to be conditioned, ie heated properly. its not much good with nz heat per room which gives and lower average temp.

tweake

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#3082426 30-May-2023 15:10

photon:

If the incoming air is 4 and outgoing is 20 and assuming equal volume goes in and out (i.e. 100% balanced), then at 100% heat exchange efficiency these two streams can do at best is to level each other to the same temperature, which would be 12 degrees. With 80% efficiency the exhaust will be warmer (~14-15) than the the incoming air (~9-10). I do not see how the incoming air can become warmer than the exhaust, physics would not allow it unless there is a powered mechanism to extract heat from the outgoing with some sort of phased coils, but it is not a thing in cross flow heat exchangers.

the heat exchangers are counter flow, so the hot outgoing air at the start is heating up the pre warmed air just about to exit into the house. its heat exchanges that go in the same direction that tend to make the temp half of the difference.

mdf

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#3082454 30-May-2023 17:22

Do professional / independent HVAC consultants or engineers exist in the NZ retail market?

I'd love a system actually designed to suit my house, and am happy to pay for such a service. However I've only ever really managed to find people primarily interested in spruiking their system.

tweake

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#3082504 30-May-2023 17:39

mdf:

Do professional / independent HVAC consultants or engineers exist in the NZ retail market?

I'd love a system actually designed to suit my house, and am happy to pay for such a service. However I've only ever really managed to find people primarily interested in spruiking their system.

in residential, i doubt it.

certainly in commercial where there is more $$$ involved, but they are also working on different buildings with different needs and different construction.

plus residential is still fairly new here. even a lot of the nz "experts" that are in the media get things wrong. we are learning to crawl here and have a lot of catching up to do. a big part of it is our housing standards have been so bad for so long, heating/aircon whole houses is still a fairly rare thing. i still get given a hard time for being "extravagant" because i have 3 heat pumps.

Handle9

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#3082513 30-May-2023 17:57

mdf:

Do professional / independent HVAC consultants or engineers exist in the NZ retail market?

I'd love a system actually designed to suit my house, and am happy to pay for such a service. However I've only ever really managed to find people primarily interested in spruiking their system.

Yes but it's relatively expensive.

There's nothing specific about residential HVAC design compared to commercial HVAC design. Air is air, energy is energy.

Design/build is far more common, which for a tiny system like a residential system is generally fine.

There are plenty of consultants doing residential design but you have to pay for it. Most people aren't interested in adding $5-10k of cost onto a residential project so it's mostly done at the high end. It's the same for mechanical contractors, most people aren't interested in paying a good contractor what they are worth when they get a contractor who has done a 3 day block course.

It's no different anywhere else in the world, building and design standards exist for that reason so contractors can pick from a range of standard solutions without adding significant cost to fairly standard projects.

timmmay

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#3082518 30-May-2023 18:17

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.

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