Does an HRV system actually "dry" the air?

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mattwnz

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#1113585 22-Aug-2014 17:28

joker97: i'd just spend the money on heatpumps. but that's me.

You did used to be able to get these ventilation systems that had a heating unit attached, not sure if they still do them, but they wouldn' t be as effective as a heat pump.

I think you get more bang for your buck with heatpumps. I think a ducted heatpump which is drawing air from elsewhere is possibly a good solution, but they are fairly pricey. But you get what you pay for. Make me wonder a bit why these companies haven't come out with their own combined system to compete against these ventilation companies, and also heavily market it.

mattwnz

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#1113587 22-Aug-2014 17:32

Niel: (e.g. sealed down lights and draft stoppers, especially for bathroom fans and range hood extractor fans as it is just a 125mm hole in the ceiling ducted to the outside)

Those are good points. If you have lots of holes in your house, the effectiveness of these positive pressure type ventilation systems maybe reduced a lot. Older downlighters for example have huge holes in them, and if you have 100 -300 of those in a house (yes there are houses with that many downlighters), you are going to need a huge fan to cause any positive air pressure change, because the house will leak air like a seive.

Jeeves

301 posts

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#1114944 25-Aug-2014 09:23

Niel: No, the air will certainly not be dry (except for some/few parts of the country). The reason why I say this is because as an example in Auckland the humidity virtually never drops below 80%. In December it never drops below 90%, typical is over 95%. This is far from dry, and without removing moisture there is no way that air will become dry. Slightly dryer yes, or rather less humid, but certainly not dry. Actually this makes product warranties interesting, because e.g. LCDs are specified to be used below 70% humidity.

I'm sorry but this is incorrect. Auckland's annual average RH is in the high 70's, with December being 75 and last year only reaching into the 90's on 2 days. This taken from NIWA's database, for the Albany area.

HRV's are ok for the right situation, but these days the right situation isn't all that often.

Niel

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#1115430 25-Aug-2014 18:43

Jeeves:
Niel: No, the air will certainly not be dry (except for some/few parts of the country). The reason why I say this is because as an example in Auckland the humidity virtually never drops below 80%. In December it never drops below 90%, typical is over 95%. This is far from dry, and without removing moisture there is no way that air will become dry. Slightly dryer yes, or rather less humid, but certainly not dry. Actually this makes product warranties interesting, because e.g. LCDs are specified to be used below 70% humidity.

I'm sorry but this is incorrect. Auckland's annual average RH is in the high 70's, with December being 75 and last year only reaching into the 90's on 2 days. This taken from NIWA's database, for the Albany area.

HRV's are ok for the right situation, but these days the right situation isn't all that often.

http://weatherspark.com/history/32738/2013/Auckland-New-Zealand
On this page is a graph of min and max humidity for Auckland. Humidity gets absorbed easier than it is released, as the moisture molecules "stick" to it. You need to look at the maximum. Within your house you also have a range of humidity, moisture evaporating where the sun shines and condensing on the cold side of the house. Maximum humidity matters (in a house).

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bfginger

1267 posts

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#1116805 27-Aug-2014 19:59

Jeeves:
Niel: No, the air will certainly not be dry (except for some/few parts of the country). The reason why I say this is because as an example in Auckland the humidity virtually never drops below 80%. In December it never drops below 90%, typical is over 95%. This is far from dry, and without removing moisture there is no way that air will become dry. Slightly dryer yes, or rather less humid, but certainly not dry. Actually this makes product warranties interesting, because e.g. LCDs are specified to be used below 70% humidity.

I'm sorry but this is incorrect. Auckland's annual average RH is in the high 70's, with December being 75 and last year only reaching into the 90's on 2 days. This taken from NIWA's database, for the Albany area.

HRV's are ok for the right situation, but these days the right situation isn't all that often.

Albany would be one of the drier parts of Auckland. NIWI's website lists an average of 82.3% for Auckland which is probably from a weather station in inland central Auckland. Coastal and western areas would go higher.
http://www.niwa.co.nz/education-and-training/schools/resources/climate/humidity

ovipop

34 posts

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#1116838 27-Aug-2014 20:43

Quote from a heating specialist: "HRV is an expensive way of opening the windows".

Jase2985

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#1116958 28-Aug-2014 06:25

ovipop: Quote from a heating specialist: "HRV is an expensive way of opening the windows".

yes and no

do you want to go to work/sleep at home with your windows open? it solves those problems and also prevents massive drafts.

when do you get the most condensation? at night, when are you least likely to have your windows open? at night, when is a hvr type system most benificial? at night

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linw

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#1117008 28-Aug-2014 08:24

At night when it is pumping cold air into the house.

timmmay

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#1117016 28-Aug-2014 08:37

I prefer double glazing (personally I have the cheaper kind, rigid 3-4mm thick panels inside the main window) to prevent condensation, with a ventilation system running through the day. Open windows require a breeze, which almost never happens in Wellington ;)

Amosnz

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#1117070 28-Aug-2014 09:23

mattwnz:

From what I have been told the fibreglass particles can be so small that they need a very very fine filter. Not sure there has ever been any testing on the effectiveness of these filters. The new fibre glass is bio soluble, but the old stuff that many people have installed may not be.

I'm about to replace the filters on my Smartvent Synergy (Balanced Pressure) system this weekend. Both the G3 filters from the heat exchanger and the finer F7 filter from the ducting.
I'll post pics of the the old and new to show what they stop (there's no fibreglass in my roof though).

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ovipop

34 posts

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#1117159 28-Aug-2014 11:06

I _strongly_ recommend also consulting a heating specialist _before_ installing an HRV.

They can explain you really well how a heating system works - they pointed out that the HRV outlets were in the wrong place - above the room door - this means the "dry" warm air doesn't flow through the room - it gets out through the door instead.

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