I've yet to have any SAP calculations but our new build will be built at least to current building regulations - better wall and roof U values offset probably by the window area (a reasonable amount north facing to take account of the views) and as air tight as reasonably possible

But I am groping a bit about ventilation and heat recovery (I'm not taking into account the relative moisture, dust, pollen advantages that the higher equipment specs have)

- the low tech approach of trickle vents and ventilators. Meets the KISS principle but feels wrong when all the effort that has gone in to insulation and air tightness

- some sort of passive system but that involves a lot of ducting work and a quote I've had was in my view extremely expensive

- the "breathing window" system which has distinct cost advantages but instinctively doesn't feel like a whole house ventilation solution (even with all the inter room vents etc). Is the superficial appearance like a big noisy warmish fan heater? (Are these units taken into account in the SAP calculations by the way?)

- a MVHR system which again is expensive and involves a lot of duct work with the net result of gaining some warmish air blowing into certain room at high level (but with the tendency of being sucked straight out again?)

Then what do you do on top of this for space heating? (this is not enough even for Passivhaus if I understand it correctly)

- use all the ducting for a warm air system by boosting the hot air through a connected ASHP (very expensive) or by some sort of post heating system with a hot water coil fed by a gas boiler/hot water tank

This means though that the ducting has to be really comprehensive (cross overs etc?) to ensure every room is heated. In addition the warm air is coming into each room at high level. Mrs Argy will be complaining about her tootsies on a cold winter's night and I'm not sure about hot air heating as a principle with it's hot points, convection currents etc - especially as the move is to under floor heating with exactly the opposite

- or, ignore a good part of that investment in HRV and just go for underfloor or conventional central heating on top accepting that you have a bit of heat recovery (although does this manifest itself by the HRV unit blowing out cool air on cold days - with the seemingly opposite effect of what was intended?)

Or - on the basis that for six months of the year none of this has a whole lot of relevance, so just go with the low tech trickle vents etc remembering to close them when there is a gale coming into the room and opening them when you're about to pass out through lack of oxygen!

Seriously I would more than welcome your views and if my thoughts are naive please don't be too hard!





-

Posted By: tonyset targets for u-values, air tightness, well better than regs, do a heat loss calculation then make decisions.

Yes, without number to base a decision on you can't really tell what to do.

Argy

You will need a ventilation rate of 0.3 to 0.5 airchanges per hour (not to be confused with an airtightness test figure which is in m3/h/m2) to provide sufficient ventilation for occupancy, otherwise the house environment will get stale and whiffy.

Your choice is whether to provide this by trickle vents and natural ventilation (100% loss) or by MVHR at say 10% loss plus the running costs of the fan. If MVHR install a system with a Specific Fan Power as close to 0.5 as you can afford.

The breathing window concept can ventilate a whole house, not just the room it's in. Leave the internal doors open and absolute humidity will stabilise throughout the house and CO2 will diffuse.

Posted By: argyThen surely you need "duct in" as well as "duct out" to say the kitchen - otherwise the space is unheated

No, that's not so really, the warm air is drawn slowly from the rooms with an inlet towards the extract vents so the temperature is fairly even. Additionally kitchens and bathrooms, when in use, tend to generate extra heat.

Be interesting to hear more about the "breathing window" .

Posted By: argyThen surely you need "duct in" as well as "duct out" to say the kitchen - otherwise the space is unheated

As RobinB says, the idea is that if you insulate to Passivhaus standards then heat will move from rooms with air supply to those with air extract. However, the air movement brought about by MVHR is typically still not enough to heat rooms with air extract to the same level as those with air supply. The air supplied to habitable rooms is typically at around 50 degrees C, while that moving between rooms will be at around 21 degrees C. In addition, people typically expect bathrooms to be at a higher temperature than habitable rooms. This is why a Passivhaus heated through the supply air will typically also have heated towel rails in the bathroom.

While I like the simplicity of the Passivhaus supply air heating approach, it does have its complications (like the need for insulated ducts) & I much prefer keeping ventilation & heating separate. A compromise may be to have underfloor heating downstairs, supply air heating to bedrooms & heated towel rails for bathrooms, However, especially if using a heat pump of some type, it pays to avoid heat emitters with different flow temperature requirements & to keep the heating flow temperature as low as possible. So, even for a build to Passivhaus standards, I would be tempted to forget the supply air heater & use underfloor heating to all areas.

Posted By: argyjust go for underfloor or conventional central heating on top accepting that you have a bit of heat recovery (although does this manifest itself by the HRV unit blowing out cool air on cold days - with the seemingly opposite effect of what was intended?)

This can happen with MVHR units which don't include frost protection heaters.Typically they mix extract & fresh air supplies, take pre-heated air from the space where the MVHR is installed or simply open the summer bypass to avoid freezing the condensation in the heat exchanger.

If you specify a simple electrical resistance heater on the fresh air inlet of the MVHR then this will protect the heat exchanger from frosting, keep the air supplied to habitable rooms at close to room temperature and only cost ~200kWh per annum to run.

David

http://www.sankom.pl/online/purmo/calculator/index.php

A couple of temp vs. efficiency graph:

http://www.rvr.ie/Advice/Specifiers/Weather_Compensation/

The attached pic is from http://www.diynot.com/forums/viewtopic.php?p=1834137

<blockquote><cite>Posted By: argy</cite>- does anyone actually have experience of using one?
- are they visually intrusive and where do you install them? (hardly a design intended to blend in)?
- are they noisy?
- as there are only two units in a house to achieve the ventilation rate does that mean they have to throw out an awful lot of air?
- and I guess that must be cool air if it was cold outside. This would feel odd and would need the main heating system at a boosted level in the vicinity to compensate"</blockquote>

Q1 - Good pics of them on-line - yes I would say, but was going to use Wilmslow Audio (look up on-line) to make some 'speaker cabinets' to put them in - unfinished MDF at around £50 each.
Q2 - not a good Q argy, define noisy! Noise stats were on-line I seem to recall. They argue that clever as it is (and it is) it is genuinely silent (I define as less than 13dB @3m for middle aged person) for long periods of time, I have discovered that my family consider 20 dB @3m utterly unacceptable anytime so would have insulated said 'speaker Cabinets'. But can be put in any available cupboard suitably amended.
Q3 - iaw Bldg Regs of course but also variable depending on its CO2 and Humidity sensors - the better the house (eg passive house) the more appropriate this unit could be IMHO.
Q4 - Argy, taken in isolation, this Q suggests you don't understand the first principles of Heat Recovery (HR), this Unit is seriously sophisticated and advanced but also specialized and should not be considered as a purchase by someone who has not informed themselves in this area. It could also be the reason you did not get a reply, as it could easily be considered that you are not a genuine potential customer - sorry to tell you like I see it and I hope you are not offended by my honesty. It was also answered above by DavidFB, starting with "This can happen..." answer being it is always (should always) be designed out. Meanwhile, speaking blindly, for sure the FW-HRV does something about this.

By comparison, I sent a series of Qs to VikH in the UK and received a sub-24hr reply.

I am not qualified to have a strong opinion on your situation but FWIW a new build that just about meets current regs is not very air-tight (ie in the context of this forum - leaks like a sieve!) and would probably not indicate the FW-HRV. 2 x FW units equates to very little saving over an entirely adequate MHRV system when 'designed in' to a new build and 'built in' as it is built. Your first reply was from Tony (who is most certainly qualified to comment!) and you should do exactly as he says. Good luck!