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15032 posts

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  # 1368769 18-Aug-2015 18:30
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scuwp:
michaelmurfy: I was quoted $3200 for a DVS system with one fan unit, 1x heated vent, 4x standard vents.

Was quoted $3400 for the same sort of unit from Smartvent.

HRV I never got a quote from as their sales strategy was so poor.


Just make sure you are comparing apples with apples.  The DVS system we looked at they didn't use acoustic ducting (which is more expensive).  We got the SV04 with 2 extra outlets and extra ducting to reach the larger areas.  $3,800 installed.  HRV insisted we needed 2 motors and wanted just on $6,000.  


That is a good point, they are noisy , espeically if you have vents in bedrooms. I have a duct outlet in my room, which I have screen closed because not only does it cause the room to get cold, but it is noisy enough to bother me. I have a tivo in my room too, and that is quiet compared to the ventilation system noise.

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  # 1368774 18-Aug-2015 18:45
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mattwnz:
Except they are expensive to run, and they don't have a long life. I have two, mitsubishi, and both no longer work as the refrigerant has failed. I had one fixed, and it worked for a few months, but then stopped working again.


You get heat from them, and for the bathroom one the results are quicker and cheaper than a heated towel rail as far as drying out towels. That saves on washing and drying costs. I buy the cheapest ones around. They last as long as anything with a cheap fan in it does. Its always been the fan that fails not the refrigeration. 140 watts of dehumidifier delivers more than 140 watts of heat because of some stuff to do with condensing water. Thats less heat needed from other appliances so the actual cost of running it in winter is probably zero.


But I would agree that when they work, they do work well, and preferable to a ducted positive pressure ventillation system, which was already installed in my house. All that seems to do is pump cold air into the rooms from the roofspace, and the dehumidifier still draws a lot of moisture out of the air.


I will have to dig the figures out, but I had a less total power usage for heating and dehumidifier in one room at mums place than for heating and having the HRV running in that room. But I will give the HRV this, it is a lot quieter than a dehumidifier.




Richard rich.ms

 
 
 
 


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Ultimate Geek


  # 1368847 18-Aug-2015 21:05
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I can't comment on an HRV system but our DVS is awesome and I would not own a house without a ventilation system now. The house is dry, easy to heat and our health improved as a result. Our system is pretty basic, just two vents, but it does the trick.

100m2 1950's weatherboard house, insulated roof and floor, single glazing.


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  # 1370741 20-Aug-2015 10:18
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Great advice from EECA - for a tropical climate. 

Not so good when it might be only 12 degrees outside during the day (as is the case over most of NZ on a cloudy winter day).

Also an effective way to let unwanted animals into the house such as  mice, the neighbour's cat or opportunist thieves (the kind that look for houses they can enter without breaking anything).

They even advise keeping  the bedroom window open overnight - there could be a 2 degree frost outside, with the added bonus of letting more noise in.

mattwnz: People could just open their windows to ventilate their homes, which is what Ecca recommend.




Mike

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  # 1371497 21-Aug-2015 11:45
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MileHighKiwi: I can't comment on an HRV system but our DVS is awesome and I would not own a house without a ventilation system now. The house is dry, easy to heat and our health improved as a result. Our system is pretty basic, just two vents, but it does the trick.

100m2 1950's weatherboard house, insulated roof and floor, single glazing.



I have to agree and can not praise our DVS system enough. I suffer with asthma and the benefits of a DVS system keeping the house dry has made a substantial and noticeable improvement to my health.

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  # 1371510 21-Aug-2015 12:08
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I haven't bothered to read the 6 pages, but add me to the list of very satisfied customers.

We installed DVS in our previous house (1960's, single level, 125m2 in Northland, Wellington with one fan unit and 4 vents) and it was the best money we have ever spent. Using four towels to wipe condensation every morning down to nothing in the space of two days.

We had a year in our current house before installing an HRV (1960's, single level, 140m2 at Otaki Beach, Kapiti Coast with two fan units and 6 vents). We have cloudless blue skies today, as always :), the outdoor air temperature is 12C, the roof space is 25C and the house is currently at 18C. We wont have the wood burner on until 5/6pm tonight to just run over night.


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Ultimate Geek


  # 1371555 21-Aug-2015 13:01
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did I just see a turn of tides? influx of positive feedbacks on these positive pressure ventilation system?

you still need to provide a way for the damp air in the house to escape, meaning you'd need to say leave a window ajar?

my dehumidifier shows humidity of 55% still I see condensation on windows on a frosty morning, I'd rather blame the single glazing, non thermal broken aluminum windows, rather than not having a dvs system pushing my warm air from heat pump out? 

 
 
 
 


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  # 1371611 21-Aug-2015 14:04
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hangon:

you still need to provide a way for the damp air in the house to escape, meaning you'd need to say leave a window ajar?

my dehumidifier shows humidity of 55% still I see condensation on windows on a frosty morning, I'd rather blame the single glazing, non thermal broken aluminum windows, rather than not having a dvs system pushing my warm air from heat pump out? 


unless your house is 100% air tight which i doubt many that were built before 2000 are there are always little gaps for the air to escape.

just remember that at night when the roof air is cold they ramp the fan right down to as low as it goes, so you could bearly feel anything coming out the vent, but its enough to stop condensation.

got home today and its 21 in the living room but 17 in the bedroom, but 26 in the roof. Crank the DVS fan up and pump all that warm air into the house, will probably be a nice 22-23 degrees inside when the sun goes down, and still about 17-18 when we go to bed.

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  # 1371630 21-Aug-2015 14:42
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Jase2985:
hangon:

you still need to provide a way for the damp air in the house to escape, meaning you'd need to say leave a window ajar?

my dehumidifier shows humidity of 55% still I see condensation on windows on a frosty morning, I'd rather blame the single glazing, non thermal broken aluminum windows, rather than not having a dvs system pushing my warm air from heat pump out? 


unless your house is 100% air tight which i doubt many that were built before 2000 are there are always little gaps for the air to escape.

just remember that at night when the roof air is cold they ramp the fan right down to as low as it goes, so you could bearly feel anything coming out the vent, but its enough to stop condensation.

got home today and its 21 in the living room but 17 in the bedroom, but 26 in the roof. Crank the DVS fan up and pump all that warm air into the house, will probably be a nice 22-23 degrees inside when the sun goes down, and still about 17-18 when we go to bed.


wasn't that draught proof the first step to retain the heat? with the weather strips, and door draft blockers

it still won't be 100% air tight, but what does a positive pressure system actually do to prevent condensation? in theory it push the "staled damp" air out of the house, using "warm dry" air from ceiling.

if the fan barely push any air during the night, how many air changes per hour can it achieve, and how does it push the damp air out of the house?

I love the idea of a (balanced) ventilation system, just not sold on a positive pressure system... and according to the salesman it won't help much during summer even with the bypass. I ended up buying a 3 room ducted heatpump which was less than 1k more than the ventilation quote.

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  # 1371637 21-Aug-2015 14:57
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window strips/door draft blockers dont stop 100% of the air getting in and out.

dont know how many changes it can do, but like it have said its enough to push the damp moist air out, as our windows dont have anywhere near as much condensation on them now then prior to the DVS.

im not trying to sell you the product. im just telling you that we had a tonne of condensation before the system, now we have next to none and no puddles on the window sils.

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  # 1371638 21-Aug-2015 14:58
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bfginger: Winter total humidity levels are much lower in the UK than here. And they have central heating so their houses are warmer.

Double glazing can reduce relative humidity by making the house warmer but although condensation may not appear on the glass that doesn't always mean the humidity has been reduced to a healthy level. Double glazing can hide high humidity. Single glazed aluminium windows will have little condensation if the relative humidity is at the levels it should be.

Opening a window to ventilate doesn't work very well in New Zealand. In the colder parts of the country you're losing huge amounts of heat. In the warmer parts like Auckland it can be so damp the relative humidity level will still be too high inside most of the time. Opening windows in many northern houses just lets mould smells out in winter.


Sorry, but I'm calling BS on the humidity thing unless you have some numbers to back it up.  Firstly because I've lived in both countries and it doesn't seem right.  Secondly, the figures I can find say otherwise:
UK humidity
Auckland humidity

The fact is, if you have a cold surface (single-glazed window, bottle of beer, etc) in anything but very dry air, it will get condensation on it.  To stop this, you either create a draft (HRV) or remove the cold surface (DG).  NZ needs to get away from this "we're a warm subtropical damp place" attitude and properly heat and insulate houses - which you are seeing now as DG is mandatory on new builds.

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Ultimate Geek


  # 1371665 21-Aug-2015 15:30
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Jase2985: window strips/door draft blockers dont stop 100% of the air getting in and out.

dont know how many changes it can do, but like it have said its enough to push the damp moist air out, as our windows dont have anywhere near as much condensation on them now then prior to the DVS.

im not trying to sell you the product. im just telling you that we had a tonne of condensation before the system, now we have next to none and no puddles on the window sils.

not saying you are selling the product - or questioning your claim that it solved your condensation issue.

I just want to get some numbers to "explain" that to myself.

say indoor temperature is 18 over night, and 8 in the ceiling.

if it does, 0.4 ACH during the night, meaning the air in the entire house is replaced every 2.5 hours, with air from ceiling - but what would that result in temperature drop (without a heat exchanger)?

on the other extreme, if it does essentially 0 ACH50 during night, would that bring any measurable reduction in humidity?

I did see ppl here claiming positive pressure system solved their condensation, and possibly more than ppl claiming it's useless. I know each house is different, I just need some simple numbers and physics to explain how does that work.

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  # 1371692 21-Aug-2015 15:40
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hangon:
Jase2985: window strips/door draft blockers dont stop 100% of the air getting in and out.

dont know how many changes it can do, but like it have said its enough to push the damp moist air out, as our windows dont have anywhere near as much condensation on them now then prior to the DVS.

im not trying to sell you the product. im just telling you that we had a tonne of condensation before the system, now we have next to none and no puddles on the window sils.

not saying you are selling the product - or questioning your claim that it solved your condensation issue.

I just want to get some numbers to "explain" that to myself.

say indoor temperature is 18 over night, and 8 in the ceiling.

if it does, 0.4 ACH during the night, meaning the air in the entire house is replaced every 2.5 hours, with air from ceiling - but what would that result in temperature drop (without a heat exchanger)?

on the other extreme, if it does essentially 0 ACH50 during night, would that bring any measurable reduction in humidity?

I did see ppl here claiming positive pressure system solved their condensation, and possibly more than ppl claiming it's useless. I know each house is different, I just need some simple numbers and physics to explain how does that work.


You've got to remember that the system is working 24/7. It's doing the majority of its work during daylight hours when the ceiling space air is warmer and the fan is not being stepped down (depending on what temp you have set the step down point at or if you use it at all). That warmer drier air is helping to reduce the relative humidity levels throughout the day and in to the night.

Sure if the system is not performing any air changes at all throughout the night then of course humidity levels will rise compared to the previous day but the house is already drier during the night than it was prior to the system going in so it's unlikely to be at levels experienced prior.

We have our system step down at 9 degrees. It's only dropped below that twice in the almost two months we've had it in (even though we've had a few frosts) and even on those frosty nights when it has stepped down at some point in the night, we've managed just a small hazing of condensation on one window in our master bedroom and that's with myself, my pregnant wife and two dogs all sleeping in the room with the door closed.

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  # 1371695 21-Aug-2015 15:55
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bcourtney:
You've got to remember that the system is working 24/7. It's doing the majority of its work during daylight hours when the ceiling space air is warmer and the fan is not being stepped down (depending on what temp you have set the step down point at or if you use it at all). That warmer drier air is helping to reduce the relative humidity levels throughout the day and in to the night.

Sure if the system is not performing any air changes at all throughout the night then of course humidity levels will rise compared to the previous day but the house is already drier during the night than it was prior to the system going in so it's unlikely to be at levels experienced prior.

We have our system step down at 9 degrees. It's only dropped below that twice in the almost two months we've had it in (even though we've had a few frosts) and even on those frosty nights when it has stepped down at some point in the night, we've managed just a small hazing of condensation on one window in our master bedroom and that's with myself, my pregnant wife and two dogs all sleeping in the room with the door closed.

thanks, that makes good sense

I suppose that might also explain why it's not working so well for some, assuming for them majority of the moisture is created from late night cooking and bed time shower, and it would be too late for the dvs to push all the damp air out.

The next thing I'd check would be comparing the humidity level in the ceiling and in the house. Still not committed without a heat exchanger though.


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  # 1371701 21-Aug-2015 16:04
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hangon:
bcourtney:
You've got to remember that the system is working 24/7. It's doing the majority of its work during daylight hours when the ceiling space air is warmer and the fan is not being stepped down (depending on what temp you have set the step down point at or if you use it at all). That warmer drier air is helping to reduce the relative humidity levels throughout the day and in to the night.

Sure if the system is not performing any air changes at all throughout the night then of course humidity levels will rise compared to the previous day but the house is already drier during the night than it was prior to the system going in so it's unlikely to be at levels experienced prior.

We have our system step down at 9 degrees. It's only dropped below that twice in the almost two months we've had it in (even though we've had a few frosts) and even on those frosty nights when it has stepped down at some point in the night, we've managed just a small hazing of condensation on one window in our master bedroom and that's with myself, my pregnant wife and two dogs all sleeping in the room with the door closed.

thanks, that makes good sense

I suppose that might also explain why it's not working so well for some, assuming for them majority of the moisture is created from late night cooking and bed time shower, and it would be too late for the dvs to push all the damp air out.

The next thing I'd check would be comparing the humidity level in the ceiling and in the house. Still not committed without a heat exchanger though.



A large amount of moisture is from people breathing. Very little should be from the shower, if it is mechanically vented, and the door is left closed. Nor cooking if your rangehood is properly vented to outside, rather than not doing any veenting outside. I have seen some that ventedinto the roof space, and was installed by muppets.For those concerned about leaving windows open, you can also now get sliding ventilation strips on aluminum windows. We had these installed when we built a new house, and they seem to work ok.

Part of the problem in newer houses, compared to older ones, is that in old houses, you used to have open fireplaces, which help to vent the house. These days houses tend to be totally sealed, and thought wasn't given to how to replace the air, which was previously done naturally. People need to look at what europe do for their eco houses.

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