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  1. #11
    Join Date
    Apr 2006
    Posts
    4,018

    Default

    Hi Dave,

    As far as I know, the DVS-type systems are not very efficient at heating. My parents had one installed in their house, and while it did a wonderful job of controlling condensation, it was not designed for heating My parent's house has since burned down, and it is just about rebuilt. They have had the DVS reinstalled, but have added a heat pump for heating. (Lesson=DVS are not designed for heating.) They are marketed as being a good way of transferring the warm air from the ceiling cavity down into the house on sunny winter days, but I think that this is a secondary benefit. It is true - they only transfer air into the house when the air temperature in the ceiling cavity is above a certain threshold. But the purpose of having this thermostatically-controlled fan is not to heat the house. It is to shut the fan off when the air temperature in the ceiling falls below a certain level, so that cold air is not pumped into the house. The main purpose of a ventilation system is to replace moist air with dry air.

    BusyLizzy's comments are all true, in my experience. New houses are better insulated, and tend to have rangehoods, extractor fans in bathrooms and laundry, and quality heating. These factors significantly reduce the ambient moisture, so there will be less condensation in new houses to begin with. My wife and I built a new house 7 years ago - we have since shifted to a 1950's built house. In both houses we had/have a logburner for heating, so there is not unflued gas heating contributing to ambient moisture. We did have mild condensation problems in the new house we built. We fixed this by installing a heat transfer system. A heat transfer system works almost identically to a ventilation system - the only difference is that the former draws heated air from the main heated area in the house (rather than the roof cavity)and redistributes this (via insulated ducting) to the colder rooms in the house. That cold air is then forced (through/under doors) back into the heated room, creating constant airflow.

    The heat transfer system is cheaper than a ventilation system. It also avoids the problem of contamination that drelly mentions. (Actually, I don't think that contamination is a genuine issue. The combination of appropriate filtration, together with the fact that the air in the ceiling cavity is drawn from outside, negates this issue.) Another benefit of the heat transfer system is that it avoids the need for localised heating. This means children's rooms can be kept warm without the worry of having heaters in them.

    My theory about how these systems work to control condensation is that they create a constant airflow across the cold window surfaces. the moist warm air inside doesn't have a chance to condense on the window surface, due to this airflow. reasons why a DVS-type system might not be effective, as BusyLizzy notes, may have to do with outlet placement. But if the curtains/drapes form a good seal around the window, this might cut down on the airflow across the window surface, thereby allowing condensation to form.

    Disclaimer: I don't own shares in any company that manufactures or distributes heat transfer systems!

    We do have condensation problems in our curernt house, which is something I need to address. It is nothing major, as we don't have any carpet (which seems to be the main trapper of moisture), and we have a good dry heating source.

    Paul.
    Last edited by SuperDad; 10-07-2006 at 02:05 PM.

  2. #12
    Join Date
    Nov 2005
    Posts
    3,286

    Default

    Quote Originally Posted by SuperDad
    Hi Dave,

    As far as I know, the DVS-type systems are not very efficient at heating. My parents had one installed in their house, and while it did a wonderful job of controlling condensation, it was not designed for heating My parent's house has since burned down, and it is just about rebuilt. They have had the DVS reinstalled, but have added a heat pump for heating. (Lesson=DVS are not designed for heating.) They are marketed as being a good way of transferring the warm air from the ceiling cavity down into the house on sunny winter days, but I think that this is a secondary benefit. Paul.
    Yes, this is true. They are not heaters. The ability to warm up the air as it circulates, on the more expensive models, is just that - it warms up the air which helps take the chill off. No good on a cold Dunedin winter's day but a welcome benefit perhaps as the nights draw in in April and you are not sure if it is worth the cost and hassle of turning on your normal more expensive heating unit or to put on an extra jumper.

    I do not believe they are advertised as heating appliances either.

    xris

  3. #13

    Default

    I had intended on installing a DVS system into my home, but as it was coming into winter went for two heat pumps.

    The house is now warm and dryer I don't think I will now need a dehumidifier at all.

    Heat pumps have come down in price by about half since I started looking at them last year I installed a 3.6kw and a 7kw pump for $5,000 all up.

    Steve
    Steven Goodey - CEO PropertyTutors Wellington

    www.propertytutors.com

  4. #14
    Join Date
    Dec 2004
    Location
    Beautiful Waitakere Ranges
    Posts
    519

    Default

    I got an HRV (DVS type system) installed in march and though I was a bit sceptical I must say it has worked flawlessly and surpassed all my expectations. The system doesn't generate any heat by itself, but an often overlooked point is that dehumidifying effect greatly enhances the heating capability of our existing heat source (wall mounted panel heaters).

    The humidity inside used to be quite similar to the ourdoor humidity, which was just terrible conditions to live in. Now the indoor humidityt is consistently 20-30% lower than outdoor i.e. 55% indoor when we have +80% outdoor.

    With the HRV and wall mounted panel heaters our indoor temperature has constantly been 19-22 degrees this winter - no more freezing mornings with dripping windows!

    Immigrating from Scandinavia 3 years ago, I must say I was initially shocked by how utterly cold and damp NZ houses are - I have never felt such cold in my life... I guess the difference is that in Scandinavia is gets so cold in the winter that houses simply must be well insulated, with double glazing etc in order for people to survive. So they are actually very comfortable to be in - going outside is another deal though
    High resolution Fractal Art on quality canvas: www.FractalArt.co.nz

  5. #15

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    Hi everyone,
    I have been reading through this forum for a couple of years, and I find it the most useful source of information for landlords online. This discussion on DVS system is particularly interesting as I am currently considering different options for sorting out humidity/ventilation issues in our rental units. We have a block of 4 brick & tile units in Mt Wellington, Auckland which we bought last year. The tenants are reluctant to open the windows and the units grow damp and mouldy. We have just done up a bathroom in one of the units, and I am concerned it will be a waste of time and money if we don’t undertake some steps to cure the problem.
    The property manager suggested buying dehumidifiers but admits there will be no way to force the tenants to use them.
    We plan to keep the units for a while, so I am looking into a proper “fix” for the problem. I think that legal issues regarding tenants paying the power costs can be covered in tenancy agreements when renewed. I also find a concept of “hidden” controls quite appealing, as this may prevent the tenants to constantly turn the system off.
    However I understand that this discussion refers to houses, have anyone installed DVS/HRS systems in units? Installing 4 DVS systems (even small units, and there is enough roof space) will be a considerable cost, so I am not quite sure if that is the right way to go in case of units. Your comments would be highly appreciated!
    Anna

  6. #16

    Default

    Hi Marpet

    And welcome, I had a very similar problem with 3 units on top of each other in Khandallah, Wellington.

    They got zero sun for 7 months every year.

    I got 1 Large DVS unit and built it into a cupbaord then ran outlets to all the tenants units and wired it through the mains.

    It was put on a timer so it ran for 4 hours in the middle of the day when tenants were out.
    The tenants didn't have access to the timer or on/off switch.
    Worked a treat and tenants didn't mind the one cost of electricity devided by 3 units.

    Hope this helps.

    Steve
    Steven Goodey - CEO PropertyTutors Wellington

    www.propertytutors.com

  7. #17
    Join Date
    Aug 2005
    Posts
    181

    Default

    Hi there,

    I have just installed a DVS unit into another rental. I sourced the materials from the wholesalers and including installation it cost me less than $500. It is a basic forced air ventilation system but in the 2 rentals I have installed them so far it has made a big difference. I installed them with a thermastat and a hidden on/off switch high up in a storage cupboard so it could be turned off in the summer. These were both houses 100m2 rather than units but one 100W fan was changing the air in them 1.5 times an hour. In the first one I also installed some ducting from a passive vent in the bathroom out to the soffit so the DVS also directly vents the bathroom to the outside too.

    Cheers,


    Geoff

  8. #18

    Default

    Thank you for your comments, Steve and Geoff, it certainly helps.
    Not sure that one DVS for all 4 units will be a right solution in our case, as we are thinking of unit titling the property in remote future, and it will probably pay to keep the units as self-contained as possible. As for the DIY option, I have not ruled it out, however the vendor will not give any warranty, and we’ll still have to involve trade people (my partner is not a handyman!)
    I think we should go for installing the DVS systems, and the next thing to do is to get some quotes (maybe we can get some sort of discount for installing 4 units) and compare the functionality. Thanks again for your help!
    Anna


 

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