Proper HRV(Cleanaire) vs PPV(DVS) for 1950's house

Forums › Home Workshop DIY › Proper HRV(Cleanaire) vs PPV(DVS) for 1950's house

k1w1k1d

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#284574 1-May-2021 12:17

Christchurch 1950's 3 bedroom red brick house, concrete tile roof, open plan kitchen dining living, log fire, aluminium single glazed windows, good ceiling insulation, no wall insulation, lots of window condensation in these cold mornings.

To stop the condensation we have the Cleanaire agent coming next week for an appraisal on fitting a balanced HRV system. Will also get DVS to price a PPV system.

I have read through most of the previous topics on this subject.

I have a few questions to ask, but wondering if there are others I should ask?

Is PPV better than HRV for older/leaky houses? We do have aluminium windows.

Is summer bypass available? On hot sunny days we usually keep the venetians and curtains closed to keep the sun out.

Will there be a cold draught in the bedrooms at night? WAF and DAF to consider.

Any suggestions from those with either system fitted would be appreciated. Thanks.

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#2700447 1-May-2021 12:31

Also get a quote from someone to install smartvent https://smartvent.co.nz/systems

You're not on Atlantis anymore, Duncan Idaho.

timmmay

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#2700475 1-May-2021 13:50

As I'm sure you know, PPV pulls air in from either the roof space or outside and pushes it into the house. That pushes out moist, warm air. I have one, running on a WiFi timer so it's going when I want it to, which is middle of the day in winter for 4 hours and morning / evening in summer, plus an hour here or there. It's a cheap option that can help reduce moisture. It won't fix condensation, to do that requires double glazing and ventilation - worked for our house anyway. Ceiling cavity air is sometimes warmed, often not good quality due to insulation, dust, etc, and they often use really poor filters. If you do this I suggest using outside air and a really good filter, get a filter box and put in a HEPA filter and maybe with a charcoal filter. I've used Filter Specialists for filters and they were good, can't remember where I got the filter box.

Heat Recovery Ventilation should be fine in an older house so long as it's moderately well sealed. It will probably pump air out of a central location, warm outside air with that air, and push the warmed fresh air into the house. It will of course lose 10 - 20% of the heat, so you may not want to run it 24/7. You need a good heat source like a heat pump.

Cleanaire have a good reputation. HRV would be much better, get a quote for it and decide if it's worth it over PPV for you.

k1w1k1d

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#2700531 1-May-2021 19:03

The DVS guy at recent Home Show said that their system slows down when roof temperature is below set room temperature to stop draughts in the bedrooms.

Can't find much info on the Cleanaire controls.

shk292

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#2700533 1-May-2021 19:16

k1w1k1d:

The DVS guy at recent Home Show said that their system slows down when roof temperature is below set room temperature to stop draughts in the bedrooms.

Can't find much info on the Cleanaire controls.

Surely that's kind of self-defeating, because in an insulated house in winter, the roof space temperature will nearly always be a lot less than the set room temperature?

I know I'd only fit a true HRV, the others seem smoke and mirrors, and good marketing

timmmay

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#2700559 1-May-2021 21:05

After having a PPV system for a decade I think they have value. Run them during the day to push moisture out so that at night the air can absorb moisture without already being saturated. You just turn them off at night to eliminate drafts. Whether that's built in or a $10 timer doesn't matter.

A PPV system is really basic. Filter ($30 for a cheap one $250 for a good systems), ducts ($100 - $500 depending on size), diffusers ($50 each), motor ($200 - $400). Installation can take some time though, to do a good job.

andrew75

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#2700588 2-May-2021 07:15

I'm always astounded at the cost of the 'brand name' systems -- essentially all they are is a controller a filter a fan and some ducting. Why they cost so much I don't understand.

We had a balanced heat recovery system (a DVS unit) in the old house. I was very dubious at the amount of energy the heat exchange actually managed to two move between the outgoing and the incoming air and whether it actually had any value at all. Unfortunately I never had a thermometer to measure at the time. Also the install was rather unimpressive, when I went up into the roof a couple of years later the ducting held together with duct tape had separated in a couple of areas and it had been sucking in unfiltered roof space air for who knows how long.

Have a look at the Ming Fans to see what they have on offer and give them a call. They were quite helpful when i installed my dyi heat transfer unit.

timmmay

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#2700603 2-May-2021 08:25

You don't even really need a controller, unless you want it to control fan speed. Just put a motor on a wifi timer and set it to run when you want it running. Generally don't have it running overnight when it's cold outside. Yes that might reduce condensation but at the expense of comfort. Double glazing is the solution for condensation.

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raytaylor

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#2700612 2-May-2021 09:01

I have had an HRV system for about 10 years.
It took about 3-6 months but we dont have any condensation issues at all now.

The thing I would look at is how hot does the attic get on a typical day?

With an HRV, you set the temperature you want the living space inside the house to be.

Temperature:
If the attic is hotter and the house is colder, it will suck air down into the house.
If the house is hotter and outside is colder, it will suck air in from outside to cool the house - great on a hot summer night.

If the house is colder, and outside is colder, it will shut down to a very slow idle mode. On very cold nights we just turn it off and it automatically switches on again 8 hours later.

In colder months, such as now, I turn the HRV up to 28deg and open the bathroom window slightly when I leave for work.
During the day the attic heats up and this hot air is blown down into the house.
Inside the house I want it to get as hot as possible to warm up the object mass. Anything that can store heat such as furniture, walls, things.
In the evening when it cools down, the HRV will shut off into idle mode while the object mass inside the house will slowly release that heat so we dont need to turn on the heat pump until later at night or later into the winter months.
For 30 watts an hour, this is some of the cheapest heating possible.

Moisture
The air coming down from the attic or in from outside is direct fresh air. This air is dryer than the moist indoor air. By having a constant positive air pressure inside the house, the moist air is constantly pushed out windows or any gaps such as the rangehood, doors when they are opened or under doors as it is replaced by the incoming dry (and sometimes hot) air.
So after about 3 months, the furniture, walls and everything had been dried and so we dont wake up with condensation on the windows any more.

When we use the heat pump, the air is much quicker to warm or cool because it is nice and dry. No moisture that also needs heating/cooling.

If you were spending money on your house heating then an HRV is definitely a component of a good heating plan.

Ray Taylor

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k1w1k1d

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#2700633 2-May-2021 10:09

Thanks Ray.

When you say "HRV", do you mean the positive pressure system sold by a company using that name, or a balanced system with a heat exchanger?

We have a concrete tile roof and I know that it gets very warm in the roof space, even on cloudy days. Quite unpleasant working up there on hot sunny days. So there could be quite a lot of heat we could push down into the house at times.

raytaylor

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#2700653 2-May-2021 10:40

Brand name HRV

Its not a heat exchanger - I imagine those wouldnt be very good at drying out the air or efficiently transferring the heat unless they have an active dehumidifier or heat pump in them.

Ray Taylor

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GenX

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#2700773 2-May-2021 13:17

As part of house renovations, I’ve recently completed a DIY installation of the Cleanaire CL200 HRV unit.

The house was 1979 built originally, so we brought all the insulation and windows up to spec. It’s a concrete tile roof with stone clad exterior and aluminum double glazing.

We had condensation on the new aluminum frames which was to be expected as they are not thermally broken.

Within 2 days of switching on the HRV we instantly noticed a difference. No condensation and there hasn’t been any since. After having a shower, in addition to having the extractor on I always used to open the window. With the HRV, I don’t open the window anymore.

We vent in and out through the concrete roof. Would have liked to have gone through the soffits but had access problems.

We have the optional summer bypass kit as well. The controller is very basic: on/off, summer/winter and fan speed, but to be honest its set and forget.

No issues with draughts. The units definitely working as you can feel a slight resistance when trying to close the bathroom door (which has a vent in).

In terms of Cleanaire the company. They were absolutely A1 to deal with providing me with loads of information upfront. I wanted to install both HRV and Heat Transfer (from the wood burner in the lounge). Cleanaire were really clear in explaining what HRV does and doesn’t do. For example it wouldn’t transfer the volumes of air required for a heat transfer system. I went with Mingfans for the Heat Transfer fans.

Very pleased with the warranty as well.

lxsw20

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#2700816 2-May-2021 16:26

shk292:

I know I'd only fit a true HRV, the others seem smoke and mirrors, and good marketing

What's the magic behind a true HRV that the others don't have?

timmmay

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#2700818 2-May-2021 16:34

lxsw20:

What's the magic behind a true HRV that the others don't have?

HRV stands for Heat Recovery Ventilation. HRV the company may sell an HRV system and a PPV system.

Scott3

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#2700820 2-May-2021 16:39

lxsw20:

What's the magic behind a true HRV that the others don't have?

In short the heat exchanger. Stale moist air from the room is via a heat exchange used to warm the cool, (hopefully) dry air from outside. Typically the heat exchangers are 60 - 95% efficient.

Be aware that they need a fairly well sealed house to work. No point in putting one in a drafty house.

https://en.wikipedia.org/wiki/Heat_recovery_ventilation

In addition to the heat exchanger they need twice the ductwork, fans etc to make the system work so cost is a lot higher than a positive pressure system.

The positive pressure systems simply blow filtered air into the house, allowing air to leak out of the house to make room for it.

Often branded as "heat recovery" as they draw air from the roof space (a dubious idea from an air quality perspective), which is warm in some conditions. Studies have found that the roof space is typically cold at time when one would want their house heated....

k1w1k1d

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#2700837 2-May-2021 17:45

"Be aware that they need a fairly well sealed house to work. No point in putting one in a drafty house."

This is one of the things I have to clear up with the Cleanaire installer. I have heard/read various views on this point.

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