HRV... is it worth it?

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#1367704 17-Aug-2015 07:28

richms: HRV actually installed a system in my mothers place with the intake about 2m from the bathroom fan that was venting into the roofspace.

If the idiot installers dont pick up on that being a slight problem then I dont really trust them with much.

Oh, and they also tapped into the power feed to a sensor light so if you turned that off the HRV was off. Quite handy to stop the floral shampoo smells cycling thru the whole house from the bathroom fan.

The bathroom fan should be vented outside.
I would say the first idiot was the person who put that bathroom fan in in the first place.

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#1367710 17-Aug-2015 07:52

Jase2985:
andrewNZ: I liken the PPV craze to the practice of venting bathroom fans into the roof space. That seemed like a good idea at the time too.

you can be as negative as you like about it, but in most cases it works as described. It doesn't work every time due to house layout or how the occupants use the house.

my parents had the same result as we did in the 2004 built, crying windows before DVS, not a single trace of moisture on the windows after.

just because it didnt work in your case doesnt mean it doesnt work in others and thats its a craze or a scam.

Unfortunately it usually works by pushing cold dry air into the house, increasing heating bills at night. A heat exchange system is less wasteful, but that's not really positive pressure.

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#1367713 17-Aug-2015 08:03

Jase2985:
andrewNZ: I liken the PPV craze to the practice of venting bathroom fans into the roof space. That seemed like a good idea at the time too.

you can be as negative as you like about it, but in most cases it works as described. It doesn't work every time due to house layout or how the occupants use the house.

my parents had the same result as we did in the 2004 built, crying windows before DVS, not a single trace of moisture on the windows after.

just because it didnt work in your case doesnt mean it doesnt work in others and thats its a craze or a scam.

How do i know if it will work in my case?

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richms

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#1367718 17-Aug-2015 08:16

If you can't have windows open because you are not home they make perfect sense if you get a properly priced one.

But the cash may be better put into something else like a dehumidifier or true heat recovery ventilation system. Don't buy the overpriced hrv brand just because if you do you are supporting a company that markets like a - holes.

Richard rich.ms

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#1367728 17-Aug-2015 08:50

timmmay:
Jase2985:
andrewNZ: I liken the PPV craze to the practice of venting bathroom fans into the roof space. That seemed like a good idea at the time too.

you can be as negative as you like about it, but in most cases it works as described. It doesn't work every time due to house layout or how the occupants use the house.

my parents had the same result as we did in the 2004 built, crying windows before DVS, not a single trace of moisture on the windows after.

just because it didnt work in your case doesnt mean it doesnt work in others and thats its a craze or a scam.

Unfortunately it usually works by pushing cold dry air into the house, increasing heating bills at night. A heat exchange system is less wasteful, but that's not really positive pressure.

I thought so but no. As the air is warmer and dryer coming form the ceiling during the majority of the 24hr period, the house is easier to heat, so takes less energy. There have been several nights where we definitely would have had the aircon roaring, but didn't need it. Our system changes the airflow based on user-set maximums and minimums to stop freezing air coming in overnight. If it was really a concern you can buy small in-line heaters for the systems.

3 points I will mention:

It takes some time to set up for the individual situation. Setting up the vent openings to get the correct pressure across the system and playing with the minimums and maximums takes a few days of fiddling to get it just right.
It does NOT blow like a fan heater into the house (like I was expecting). The air coming out is hardly perceptible. Even putting your hand right up to the vent you can only just feel a very gentle breeze. I was amazed this was enough - but it is. Close a door and I immediately feel a gentle breeze under the gap at the bottom with the air being forced out.
Watch where you place the motor. They are relatively quiet but if you are sensitive to noise I would not place over a bedroom or living area.

I am still a skeptic on the whole 'positive pressure' hype, but taking it as at it's rudimentary set up as 'ventilation' system I now can't imagine ever being without one.

Lazy is such an ugly word, I prefer to call it selective participation

scuwp

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#1367730 17-Aug-2015 08:54

richms: If you can't have windows open because you are not home they make perfect sense if you get a properly priced one.

But the cash may be better put into something else like a dehumidifier or true heat recovery ventilation system. Don't buy the overpriced hrv brand just because if you do you are supporting a company that markets like a - holes.

I agree they are overpriced, so shop around. If you are even remotely handyman capable they are not hard to install, just think carefully about where the vents go, and get a sparky to do the final wiring. We got them to install ours and they did have some specific theories about vent locations, for example NEVER in a bathroom or wet area, and not too close to the windows.

Our dehumidifier has been put in the garage and is now collecting dust. It has been made redundant.

Lazy is such an ugly word, I prefer to call it selective participation

RunningMan

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#1367736 17-Aug-2015 09:05

I think ultimately it's going to depend on the construction of the particular house as to whether there is any benefit.

Firstly, how much natural ventilation is there currently? Old houses with poor fitting windows and doors and open chimneys naturally have reasonable passive airflow already, so won't need a lot of additional ventilation. Newer houses are far better sealed so don't naturally breath so benefit more from forced ventilation.

Secondly, what is the source air actually like? Get up in the roof space and check for yourself. Is it better than what's in the house - if not, then why blow it in? Roof construction will mean some houses are a lot warmer in the roof space, and will benefit, others are cold and draughty and all you do is blow cold air inside, displacing already warm air. What is the external humidity like compared to inside? Eg. Auckland can be far more humid than other parts of the country, so the external air is likely to already have a lot of moisture in it, reducing the benefit (dehumidifier may be a better option in this case), but if the external humidity is low, then introducing much drier air is a good thing.

Look at the existing ventilation, and compare the internal and external air quality to see if this sort of system will be beneficial to your situation.

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Wade

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#1367738 17-Aug-2015 09:12

timmmay:
Jase2985:
andrewNZ: I liken the PPV craze to the practice of venting bathroom fans into the roof space. That seemed like a good idea at the time too.

you can be as negative as you like about it, but in most cases it works as described. It doesn't work every time due to house layout or how the occupants use the house.

my parents had the same result as we did in the 2004 built, crying windows before DVS, not a single trace of moisture on the windows after.

just because it didnt work in your case doesnt mean it doesnt work in others and thats its a craze or a scam.

Unfortunately it usually works by pushing cold dry air into the house, increasing heating bills at night. A heat exchange system is less wasteful, but that's not really positive pressure.

If you have the temp on the control unit at inside temp or higher the amount of air pumping through the system is so negligible you don't notice any cooling effect

bfginger

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#1367821 17-Aug-2015 10:56

Many old 1950s houses leak so much air that air passes through from outside at a faster rate than what a ventilation system does. Buy a humidistat thermostat to see what the humidity levels and temperature are inside.

Does it have stagnant air in an enclosed space under the house? Without ventilation or an evaporation barrier over the ground that space can become very damp and end up in the house. Sometimes PPV systems will suck that damp air into the ceiling and then into the house.

There are reclaim systems that can optionally use ceiling air to warm incoming air without putting the ceiling air into the house.

http://dvs.co.nz/solutions/ventilation/dvs-reclaim-ventilation-system/

http://www.cleanaire.co.nz/

Jase2985

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#1367861 17-Aug-2015 12:16

timmmay:

Unfortunately it usually works by pushing cold dry air into the house, increasing heating bills at night.

we dont use a heater at night as we have the tempervents on 2 of the outlets. The incoming air is about 10 degrees warmer than it is in the roof. And as mentioned the fan ramps right down at night so its barely noticeable that its on. but its enough that the rooms dont condensate. With out the tempervents on its slightly colder in the bedrooms but your under a blanket and we dont notice it at all and we still have reasonable clear windows in the morning.

Personal preference i guess.

richms

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#1367862 17-Aug-2015 12:16

I think the biggest benefit in PPV is if you have a damp basement and the pressure will stop the damp air convecting inside as the warm air leaves thru the ceiling.

Richard rich.ms

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#1367892 17-Aug-2015 13:07

Summarising this thread.

Blows cold air into house, stops crying Windows, May make house easier to heat

Jase2985

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#1367897 17-Aug-2015 13:28

joker97: Summarising this thread.

Blows cold air into house, stops crying Windows, May make house easier to heat

blows air from the roof what ever temp it is, be it hot, warm or cold

mdooher

Hmm, what to write...
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#1367898 17-Aug-2015 13:30

This from here: http://www.energywise.govt.nz/your-home/ventilation/systems
Roof space air or outdoor air?
Roof spaces are often polluted with dust, mould and vermin. To keep the air supply clean, positive pressure/roof cavity ventilation systems are usually fitted with filters. The quality of the air entering the house is highly dependent on the filter type and how often it is cleaned. As suppliers have yet to prove that home ventilation system filters are effective at reducing these contaminants to safe levels, EECA recommends that the supply air of home ventilation systems be sourced from the outside, not from the roof cavity. The New Zealand Building Code requires homes to have means of ventilation with outdoor air to maintain air purity. Ventilation systems that draw air from the roof space and not directly from outside do not comply with ventilation standard NZS4303:1990 "Ventilation for acceptable indoor air quality" and cannot be used to comply with the Building Code Acceptable Solution for ventilation.

Research recommends that you do not install this type of system for heating purposes University of Otago research shows that the heat available from moving roof space air into your home (as the most common type of ventilation system does) does not provide significant benefits compared with what you need to properly heat a home in winter. The research also found that pumping air from the roof space into the living area would often push internal temperatures away from the desired level, rather than toward it. In summer, roof cavities quickly become excessively hot, and systems that pump roof space air into your house without a summer bypass will have to be turned off for extended periods in order to avoid overheating your house.

Matthew

mdooher

Hmm, what to write...
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#1367901 17-Aug-2015 13:43

Or in my personal opinion... Don't be so stupid as to put one off these overpriced fans in a tube in your house. Yes it will stop crying windows, but so what? do think that makes your house healthier?

The way to remove moisture form your house is to:

1 Bring in fresh air (at least 10% fresh)
2 filter it
3 remove the moisture from it
4 heat it (particularly if you removed the moisture by cooling it)
5 recycle about 90%
5 Allow the 10% overpressure air back out (recover heat from it for efficiency)

This is what I do, we never open our windows, never have crying windows, never smell the disgusting coal fires in the rest of the neighborhood and quite frankly do a lot less dusting (well my wife does)

Matthew

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