HRV... is it worth it?

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BDFL - Memuneh
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#1371711 21-Aug-2015 16:20

We have DVS at home. House, 100 sq m, 1950s, single floor, floor and ceiling insulation. We leave high up in Johnsonville, just around the line where frost settles in (and when we had snow a few years back it actually lasted five days while everywhere else was dry already).

This means leaving windows open is an invite for a cold home in winter. DVS on during the day is a cold home too because when it's not cloudy in winter the sun goes down around 5pm which means we don't really get lots of warmth from the ceiling cavity.

What really works for us is the dehumidifier. We can fill a 6 litre Delonghi over a single day. If we put one in the bathroom overnight it's nice and dry, and warm. If we leave one in the bedroom during the day it's nice and dry and sometimes take the chill out too.

kiwirock

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#1371716 21-Aug-2015 16:24

Yes but where does the moisture get pushed in to? I've seen some nasty pictures of inside of walls where the damp has been pushed in to.

Jase2985:
andrewNZ: NO. Positive pressure ventilation is a scam.

I have just unplugged the one in my house (installed by the previous owner) and my house is now a LOT warmer with no noticable increase in condensation.

i disagree

here are some photos from my house of the windows in the morning. We have a DVS with a vent in each bedroom and one in the living space. Built in 1955, 100sqm. 700mm off the ground on piles, no insulation in the walls, minimum spec in the roof and under the floor. Weather board, tin roof and single glazed wood framed windows that leak a bit

Taken in a smallish bedroom (2.7x3m) where a single person sleeps with the door shut. the tempertaure during the day and over night was within 1deg of each other and it didnt rain either day.

With DVS (Click for larger picture)

Without DVS (was turned off for 24 hours)

It does make a difference, but the results may vary and it does depend on your house. made a huge difference in ours

kiwirock

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#1371717 21-Aug-2015 16:28

sir1963:
RunningMan:
BinaryLimited:
shrub: Just remember its a fan in a box..... But it does work very well and keeps the moisture out by forcing the dry air down.

Take it that the dry air comes from the roof,therefore i need to make sure insulation in the roof is 100%?

Ceiling insulation will make zero difference to the air in the roof space. All it's doing is sucking air from outside and blowing it through the house - it's that simple.

Not quite, the air in the roof space can be a LOT warmer than the outside air thanks to a large surface area ( the roof), good conduction into the airspace (iron roofing), and the air tends to be drier (no people breathing, now cooking, no showers etc0. So warmer, drier air is good.

HOWEVER, as someone else said, it is not much more than a box , a thermostat and a fan.

DVS/HRV/etc systems are grossly over priced.

If you're going to spend a grand or two anyway, get a system with a balanced fan system that also has an air-to-air heat recovery unit. Not just a fan that pushes out the warm air from your home and pulls in roof space air. In winter, my roof is usually pretty cold.

Avon electric make them, I think they are cleanaire.co.nz look them up or look up how air to air heat exchangers work.

They a balanced system that both pulls in fresh air from outside (not the dirty roof space) and exhaust stale humid inside air back outside. Both air streams flow in a counter direction over some aluminum plates that conduct the heat from the exhaust air, pre-heating the incoming fresh air. You don't need a roof full of wasted heat for these to work.

edit: I should add, because it constantly recycles heat (saves $$$), it also makes sure the incoming airs relative humidity is even lower before it's introduced in to the home.

hangon

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#1371730 21-Aug-2015 16:43

mattwnz:

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.

you should see my inlaws making steamed buns... that's gotta be like all black team in the changing room after a match.

agree with the 2nd part, and the issue with bathroom vent is, if no window/door are opened (during winter), then it hardly moves much air/moisture out - if it doesn't follow physics it would have sucked the entire house into vacuum.

Jase2985

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#1371777 21-Aug-2015 18:49

we loose about 4deg of temps indoors when the roof temp gets down to about 9 over night

Indoor starts at about 18degrees at about 930pm, the roof is about 15-16degrees
at 630am in the morning its 14 degrees inside and about 9 degrees in the roof. i dont consider that too bad considering. We do have 2 temper vents which is 1/3 of the actual flow into the house.

Ill try again another day with the tempervent off and see if it makes any discernible difference.

bfginger

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#1371864 21-Aug-2015 21:58

The amount of humidity air can carry increases with higher temperatures. Relative humidity approximately halves with each 10 degree celsius increase. As the UK is colder the total humidity levels are lower at the same relative humidity level. Average winter room temperatures are around 4 or 5 degrees warmer in England too.

Different parts of Auckland have different average relative humidity levels. NIWA has 82.2% as representative of the region. Damper parts of Auckland will be higher.

mattwnz

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#1371867 21-Aug-2015 22:16

The best thing people can do, is to install lots of ceiling batts, then wall batts. If you buy a new house from a developer, it will likely have been built to the minimum current standards, so if you can, get it upspeced to R 5 or R6. People seem to have a fixation on installing floor insualtion for houses on piles, but you lose very little heat through the floor so it isn't particularly cost effective compared to ceiling and wall. You are better IMO to install carpet with a good underlay if you have a cold floor Possibilly seal the ground with polythene too to reduce dampness under thr house, but the under floor space should be well ventilated too..

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Aredwood

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#1372102 22-Aug-2015 18:57

richms:
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.

"Latent heat of water" Is the reason you get more heat than just the power used. The heat energy is gained by condensing water vapour (humidity) into liquid water. You get approx 0.6kW/hr of free heat for every litre of water that your dehumidifier collects.

I always laugh at those who get those [not so] econo panel heaters. They should instead be getting dehumidifiers. For approx the same power consumption, you get extra heat. And less humidity. Compared to the panel heater.

Jaxson

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#1372257 23-Aug-2015 02:45

I'd propose heading outside and pulling a thick blanket of insulation over your roof when you get home from work each day. This will trap the sun warmed air in your roof cavity, between your ceiling insulation and the new insulation cover you've just pulled over the whole house. Without this, your free heat has been dissipating into the environment outside each night through poor roofing material insulation...

BinaryLimited

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#1372274 23-Aug-2015 07:50

freitasm: We have DVS at home. House, 100 sq m, 1950s, single floor, floor and ceiling insulation. We leave high up in Johnsonville, just around the line where frost settles in (and when we had snow a few years back it actually lasted five days while everywhere else was dry already).

This means leaving windows open is an invite for a cold home in winter. DVS on during the day is a cold home too because when it's not cloudy in winter the sun goes down around 5pm which means we don't really get lots of warmth from the ceiling cavity.

What really works for us is the dehumidifier. We can fill a 6 litre Delonghi over a single day. If we put one in the bathroom overnight it's nice and dry, and warm. If we leave one in the bedroom during the day it's nice and dry and sometimes take the chill out too.

Sounds like the power companies love you....dont the dehumidifiers eat alot of power?
If you have a fireplace in your lounge...smartvent have the heat transfer option which sounds great.

Have the same house issues as you... dvs...cold home... got a fireplace in the lounge which is ideal.

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richms

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#1372279 23-Aug-2015 08:26

Dehumidifiers are typically only a few 100 watts so no not a massive amount. Probably only add 30 bucks all up to the bill each month here. Well worth it.

They are not running all the time. They cycle on and off and then basically throttle back to near nothing once you are at the desired humidity. Unless you get a cheapie with no humidistat which will just run till the tank is full.

When they do use a lot of power is if you run them in a cold room and they have a defrost heater. But that's a problem because you have a cold room. It ends up heating the room as it defrost so won't cost much different than it would to heat the room anyway.

Richard rich.ms

Michaelfjs

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#1378247 2-Sep-2015 13:47

I'm looking at getting some kind of system like this for our house.

I had a look at smartvent.

Their smartvent-evolve system controller looks like an android tablet. Do they give you a tablet as part of the package, or is it just software which runs on an android tablet?

http://smartvent.co.nz/smartvent-evolve/

Michaelfjs

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#1378284 2-Sep-2015 14:27

Michaelfjs: I'm looking at getting some kind of system like this for our house.

I had a look at smartvent.

Their smartvent-evolve system controller looks like an android tablet. Do they give you a tablet as part of the package, or is it just software which runs on an android tablet?

http://smartvent.co.nz/smartvent-evolve/

According to the brochure;

"Your tablet can also be used for music, games, browsing or reading your emails."

So it looks like they include a tablet with the software pre-installed.

scuwp

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#1378361 2-Sep-2015 15:19

Michaelfjs: I'm looking at getting some kind of system like this for our house.

I had a look at smartvent.

Their smartvent-evolve system controller looks like an android tablet. Do they give you a tablet as part of the package, or is it just software which runs on an android tablet?

http://smartvent.co.nz/smartvent-evolve/

It includes a basic android tablet. While it looks cool and has the geek-factor we decided to save a grand and use the conventional controller. The humidity sensors is the only real difference, and requires the summer ventilation add-on to work. IIRC you can download the app and run it on any device.

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

BinaryLimited

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#1380031 4-Sep-2015 22:11

scuwp:
Michaelfjs: I'm looking at getting some kind of system like this for our house.

I had a look at smartvent.

Their smartvent-evolve system controller looks like an android tablet. Do they give you a tablet as part of the package, or is it just software which runs on an android tablet?

http://smartvent.co.nz/smartvent-evolve/

It includes a basic android tablet. While it looks cool and has the geek-factor we decided to save a grand and use the conventional controller. The humidity sensors is the only real difference, and requires the summer ventilation add-on to work. IIRC you can download the app and run it on any device.

Recently got the smartvent evolve.
Didnt get the summer package,but works fine. Tablet is lame, can take 2 sim cards tho. Really need them to publish the android app!

Is it normal for the smart vent system to turn off when the tablet isnt on????

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