Airtightness and HRV

fathersdaughter

Hi there,

Very confused about this at the moment!!

I'm currently building a very well insulated house, installing geothermal heating and low u-value windows.

Is it necessary to have the house airtight or what are my other options?

From what I understand, airtightness involves sealing up all the windows and doors with special tape, and if I do this, I will then need to install a HRV system for ventilation. Is this true?

And if I don't do this what must I do? Vents in wall or windows?? Even though the house is not airtight?

If anyone could offer me any clarification on the above or advise on the best route for my house it would be greatly appreciated!

Thanks

sydthebeat

have you any professional advising you at the moment?

the commonly held opinion is that if you are going to heat a house with geothermal Under floor heating (UFH) you should ALWAYS install a mechanical heat recovery ventilation system (MHRV).

You must provide ventilation to you house, its a regulation. The most common way of providing this is by drilling holes in your walls, these are commonly known as hole-in-the-wall vents and you see them as grills up high internally. While these provide adequate ventilation, they are very inefficient from a heating point of view. For example if you have a stiff wind blowing outside, say at 15-20 mph, these wall vents can change the total amount of air in a room approximately 4 times every hour. That means that your heating system has to heat the room 4 times every hour.

If you install a MHRV system and its running at 75% efficiency (which is actually quite low, efficiencies in the 90's are available) then what happens is every hour the air in teh room is changed once and 3/4 of the heat is put back in. so therefore, with a MRHV system, your heating system may only have to heat the room once every 4 hours (instead of 4 times every hour). That means that you can save 16 times (4 x 4) the fuel needed to heat a room if you install a MHRV system.

Also, as geothermal / heat pump runs on electricity, the harder it has to work to provide a comfortable heat, the more inefficient it becomes and thus the higher your bills will be.

If you are building at the moment you are legally required to have an air tightness test done prior to you occupying the dwelling. It would be more logical to employ someone to do two test on your houses. The first being to identify air tightness issues with the build. This can be done prior to the internal plastering.

Have you had a provisional BER assessment done to see if what you are building complies with building regulations?

BryanF

fathersdaughter wrote: »

Hi there,

Very confused about this at the moment!!

I'm currently building a very well insulated house, installing geothermal heating and low u-value windows.

1. Is it necessary to have the house airtight or what are my other options?
2. From what I understand, airtightness involves sealing up all the windows and doors with special tape, and if I do this, I will then need to install a HRV system for ventilation.
3. Is this true?And if I don't do this what must I do?
4. Vents in wall or windows??
5. Even though the house is not airtight?

If anyone could offer me any clarification on the above or advise on the best route for my house it would be greatly appreciated!

Thanks

1. current regs require you to make an effort to seal up your build, current thinking on the matter is that a huge % of your heat is lost through a lack of air-tightness and as such it should get as much attention as insulation. the 2011 regs are starting to incease the air-tightness levels and this will tighten more and more in the coming years.. mechanical ventilation is nothing to be avoiding: we already have kitchen and wc extracts so this is just the next step.. your options are: seal up the building and install MVHR, or have a mix of wall vents and extractors or DCMV which is vents in the wall with RH sensors that open on demand
2. regardless of whether you install mvhr you should try to achieve the best air-tightness you can.. there is a difference between unregulated drafts and ventilation..
3. it is true.. if you dont do this just be prepared to sit in a draft with 100mm dia holes in the wall of all your rooms or window vents..
4. yes
5. yes

may i ask as there may be time to act yet
what stage are you actually at?
have you an architect? what is he telling you?
have you done a provisional BER cert or better a Phpp (passive house) calculation?
maybe have a read of this:
http://www.passivehouseacademy.com/downloads/New-Build-Passive-House-Guidlines.pdf (I'm not saying you must go passive but this is the standard to achieve)

AMG86

Look at details re Passive House. Here are some links http://www.phai.ie/. http://www.proair.ie/index.php?option=com_content&task=view&id=70&Itemid=220. http://www.passivehousebuilder.com/. There are others. You will not regret investing time and money in getting a well insulated airtight house. Heating costs will be significantly lower than a house built to minimum standards.

about2build

Yes airtightness is a requirement for use of mvhr...It can be achieved quite easily by using say sips structured insulated panels or timber frame structure......are you intending using a masonry cavity wall build and if so what levels of insulation are you using? It is quite difficult to achieve the air tightness needed with this method....any thoughts on how it can be done from the other contributors??

fathersdaughter

Hi there,
thanks for the replies. I'm building a block house with 200 mm pumped cavity in the walls. I'm wondering is it very costly to make house airtight and how would I go about doing this?

Thanks

BryanF

if your going direct labour you need to go a do a course yourself or employ a specialist contractor to do it/advise you. if your going with the traditional route of architect and main contractor you make it their problem...:)