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534 posts

Ultimate Geek
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  Reply # 450968 23-Mar-2011 00:48
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iistudio: One of my colleaque was asking around for people's opinions on HRV Cool
I will let him know about this.......

Also anyone thinks HRV or DVS system actually
useful or say good for money spend on it?

thanks


Yes but it depends on what you are trying to achieve.

HRV & DVS are different technologies both trying to achieve the same thing.
If you have a well insulated house and are trying to manage potential moisture issues then yes go for it. We have a new house and had Smartvent put in to make sure we didn't end up with a damp new house :)




 

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  Reply # 450981 23-Mar-2011 07:24
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Shock: 


HRV & DVS are different technologies both trying to achieve the same thing.



Not really. Essentially they are both fans with a filtered inlet in your roof and some diffusers in the house. 

They have some different options but essentially that's all they are.

They are: Ventilation system.
They aren't: Heaters, airconditioners, coolers, dehumidiifers.  

 
 
 
 


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Master Geek
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  Reply # 450984 23-Mar-2011 07:45
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iistudio: 
Also anyone thinks HRV or DVS system actually 
useful or say good for money spend on it?


thanks
Purely my opinion:

http://www.geekzone.co.nz/forums.asp?forumid=48&topicid=73781&page_no=1#420350

 

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  Reply # 451009 23-Mar-2011 09:06
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iistudio: anyone thinks HRV or DVS system actually useful or say good for money spend on it?

Have a good search around the forums as this has been done many times in the past.

They should be considered ventilation devices primarily.  If you have ventilation problems then this may be for you.

You pump fresh air into your house which hopefully pushes stale/moisture laden air out.  That's the guts of it.  Often the modern house is well sealed so the air will escape back into the roof cavity via downlight penetrations.

The best ones (ie if they have this they will surely let you know and you'll pay for it) use a heat exchanger system, where air coming in gets pre warmed by air coming out of the house.  There will be some cross over months of the year when you will get warm air from the ceiling space. 

In winter though, especially at night, it's safe to say your roof will be cold and you will be pumping cold air straight into the house.  Modern houses are very well sealed to prevent draughts but here is one you are introducing yourself that bypasses your ceiling insulation and forces cold air straight into your home.  In summer when the roof is super heated, you're doing the same concept of pumping really hot air into your house.

What it boils down to is they will have their place but you need to really address why you are want/need one and get good advice.  Given what I've just read in the posts above it seems this side of it might not be happening.

gzt

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  Reply # 451087 23-Mar-2011 11:58
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My personal opinion is that most systems taking air from the roof cavity are essentially flawed. In the event of fire, they may pump rising smoke and combustion products back into the house.

At minimum these systems should incorporate a combustion product detector of some kind with a shutdown and alarm.

Also many roof cavities will have glass fibre insulation or other products. Filters are intended to take care of that, but I am still personally uncomfortable about that.

In my opinion the correct and clean way to get heat from the roof cavity is to use a heat exchanger to warm cold clean air taken from outside the house. Just using filtered warm air straight from the roof cavity seems very cheap and nasty to me. Not to say the method is not cost effective.

EECA compiled a report on home ventilation systems (2009) after concerns that some marketers were making unsupported claims. Worth a look for an overview of the issues.

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  Reply # 451090 23-Mar-2011 12:05
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gzt: many roof cavities will have glass fibre insulation or other products. Filters are intended to take care of that, but I am still personally uncomfortable about that.
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  Reply # 451091 23-Mar-2011 12:09
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We've had a similar bad experience with pushy HRV sales reps. We only agreed to seeing one because we were weighing up our heating options, and were assured over the phone that it would be a no pressure, obligation free quote.

After we had sat through sales spiel, and been given a quote of approx $7000 (which FAR exceeded any budget we may have had), he pulled out the paperwork and intended to sign us up straight away. When we told him that the cost was much more than we had anticipated, and was one we could not possibly afford, he started trying to guilt us into it ("Isn't your families health important to you?"). At point he was swiftly shown to the door.


 

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Ultimate Geek
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  Reply # 451107 23-Mar-2011 13:02
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Handle9:
Shock: 


HRV & DVS are different technologies both trying to achieve the same thing.



Not really. Essentially they are both fans with a filtered inlet in your roof and some diffusers in the house. 

They have some different options but essentially that's all they are.

They are: Ventilation system.
They aren't: Heaters, airconditioners, coolers, dehumidiifers.  




 

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Ultimate Geek
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  Reply # 451109 23-Mar-2011 13:02
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Handle9:
Shock: 


HRV & DVS are different technologies both trying to achieve the same thing.



Not really. Essentially they are both fans with a filtered inlet in your roof and some diffusers in the house. 

They have some different options but essentially that's all they are.

They are: Ventilation system.
They aren't: Heaters, airconditioners, coolers, dehumidiifers.  


Well you can simplify it like that if you want but HRV is a positive pressure system where DVS / Smartvent are not. 

PPS systems are pushing air down all outlets and out through gaps, cracks doors etc. DVS / Smartvent systems pulls wet air from wet sources (e.g. bathrooms) and outputs dry to other rooms. You can also retrieve from a room with a heat source (e.g. fire / heat pump) to feed to other rooms and assist drying. HRV cannot do that.

There was a really good thread on this somewhere here with a spreadsheet that broke down all the different systems. I used it for the basis of my research when looking into buying one of these.




 

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Master Geek
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  Reply # 451117 23-Mar-2011 13:26
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Shock: 
Well you can simplify it like that if you want but HRV is a positive pressure system where DVS / Smartvent are not. 

PPS systems are pushing air down all outlets and out through gaps, cracks doors etc. DVS / Smartvent systems pulls wet air from wet sources (e.g. bathrooms) and outputs dry to other rooms. You can also retrieve from a room with a heat source (e.g. fire / heat pump) to feed to other rooms and assist drying. HRV cannot do that.



Well I must have a very different DVS system. It performs EXACTLY like the highlighted text in your above quote.

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  Reply # 451124 23-Mar-2011 13:41
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iistudio: One of my colleaque was asking around for people's opinions on HRV Cool
I will let him know about this.......

Also anyone thinks HRV or DVS system actually
useful or say good for money spend on it?


thanks


 

I would suggest you ask an architect what their opinion is on these types of systems. I haven't seen any scientific research on them and how effective they are.

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  Reply # 451126 23-Mar-2011 13:50
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mattwnz: 

I would suggest you ask an architect what their opinion is on these types of systems. I haven't seen any scientific research on them and how effective they are.


Honestly most architects don't have a clue about mechanical systems (ie ventilation, heating etc). Generally what the care about is what the wall controllers and the diffusers look like - not how or why they do or don't work. 

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  Reply # 451129 23-Mar-2011 14:01
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Handle9:
mattwnz: 

I would suggest you ask an architect what their opinion is on these types of systems. I haven't seen any scientific research on them and how effective they are.



Honestly most architects don't have a clue about mechanical systems (ie ventilation, heating etc). Generally what the care about is what the wall controllers and the diffusers look like - not how or why they do or don't work. 


 

That is a sweeping statement. If you get a good experience one who knows their stuff, they will know a lot about ventialltion and the best options. A well designed house can have natural ventilation using the 'stack effect' and passive solar heating and cooling, which can do away with the need for such ventialltion systems anyway. These fan based ventilation systems that you install are generally a sticking plaster solution for  poorly designed and insulated houses, which make up the bulk of NZs housing stock.

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  Reply # 451130 23-Mar-2011 14:01
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Shock:
Handle9:
Shock: 


HRV & DVS are different technologies both trying to achieve the same thing.



Not really. Essentially they are both fans with a filtered inlet in your roof and some diffusers in the house. 

They have some different options but essentially that's all they are.

They are: Ventilation system.
They aren't: Heaters, airconditioners, coolers, dehumidiifers.  


Well you can simplify it like that if you want but HRV is a positive pressure system where DVS / Smartvent are not. 

PPS systems are pushing air down all outlets and out through gaps, cracks doors etc. DVS / Smartvent systems pulls wet air from wet sources (e.g. bathrooms) and outputs dry to other rooms. You can also retrieve from a room with a heat source (e.g. fire / heat pump) to feed to other rooms and assist drying. HRV cannot do that.

There was a really good thread on this somewhere here with a spreadsheet that broke down all the different systems. I used it for the basis of my research when looking into buying one of these.


Honestly I think you're a little confused. Smartvent is a positive pressure system. Securimax and DVS do do heat exchanger systems which is what you're referring to but their entry level systems are PPV.

The Securimax heat exchange system is called Synergy, DVS have another name for theirs. They have only come to the market relatively recently, and are roughly equivalent to the Mitsubishi Electric lossnay system, however their PPV systems have been around for a long time and are by a long way their biggest sellers.

With regards to heat transfer you're right, HRV don't tend to do that. Saying that the cheapest and least lossy way to that is by a stand alone system. They're pretty crap with heatpumps unless you have very well insulated ducts and short runs. The're much better with fires as fires don't modulate their outputs and are usually oversized and overheat the space. That means you've got enough spare heating capacity to afford losses through a cold ceiling space.


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  Reply # 451132 23-Mar-2011 14:06
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mattwnz:
Handle9:
mattwnz: 

I would suggest you ask an architect what their opinion is on these types of systems. I haven't seen any scientific research on them and how effective they are.



Honestly most architects don't have a clue about mechanical systems (ie ventilation, heating etc). Generally what the care about is what the wall controllers and the diffusers look like - not how or why they do or don't work. 


 

That is a sweeping statement. If you get a good experience one who knows their stuff, they will know a lot about ventialltion and the best options. I well designed house can hve natural ventialltion using the 'stack effect' and passive solor heating and cooling, which can do away with the need for such ventialltion systems anyway. These ventilation systems that you install are generally a sticking plaster solution for  poorly designed and insulated houses, which make up the bulk of NZs housing stick.


I don't install them, I don't sell them. I work in the industry and have a pretty good knowledge of how they work.

My statement is based around experience of dealing with architects who don't know what they are talking about with regards to these systems. It's not what they do - it's mechanical services engineers who are trained to design mechanical systems. Some architects have knowledge of mechanical systems but if you want to talk to an expert talk to an expert - a mechanical services engineer not an architect.

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