Notes on heat rating - ventilation

KAGY

Just some quick notes FYI regarding heat rating of buildings:

• Poorly fitted insulation can reduce the design U value by 50%
  BRE have performed research into how fitting insulation affects the U value of the house. With a typical cavity built house the U value is calculated based on these assumptions: (1) insulation is fitted tight to the internal course(we all know that no builder cleans off the mortar from this layer so your insulation is now held off the wall by this overflow) (2) insulation is a continuous layer (this isn't the case, ofter the builder just sits the insulation on the wall ties, leaving anything from a 3mm to 10mm gap, this mightn't sound big but wait till you hear the result of this!) (3) the air gap is known as a "still air gap", (this is the big one, but because of the non conformance to 1 & 2 above we have a situation where we have a layer of air heated by the house, and a layer of air cooled down by the ambient temperature separated by the insulation. But hot air rises sucking the cold air through the small gaps, thus leaving cold air next to the internal wall. The result of this, double the heat loss!
  Timber framed homes don't suffer as badly as this because the insulation is behind a OSB sheeting, reducing but not preventing this circulation, there can still be small gaps between panels. Depending on how tight the insulation is, you could be losing an extra 20% of heat through the wall.
• Open fires can cool down your house
  Think about when a fire is lit, you may know yourself the draft heading up the chimney, I've heard it likened to a 9inch ventilation fan running full speed. This air is coming from the rest of the house, and it's been replaced by cool air from the outside. The victorians knew about this, and they had vents in the fire to feed oxygen directly from the outside to the fire. You can also get valves for chimneys to close off this path to the outside when the fire isn't lit.
• Drafts can add 35% onto your heating bill
  Once again cold air from out side needs to be heated up. But we need fresh air to breath. it is recommended that we should change the full volume of air in a house at least once or twice an hour. The best way to do this is to install a heat recovery ventilation system, suck the air out of say the kitchen, bathrooms, ensuites etc, and use this to heat up the air coming in and feed this back to say the living and sleeping areas (note you don't need a feed and return in each room). Once again, savings are due to preventing uncontrolled cold air movement, and this means sealing the house.

Now find me a builder who actually cares about these things...

CJhaughey

My builder does....http://www.scanhome.ie/philosophy.php

patrido

Now find me a builder who actually cares about these things...

nice post, some very good points there. I always say that people should watch their builder like a hawk, to ensure that all the building regs, manufacturers guidelines, and good building practice are adhered to.

<2cents>
I would dispute one small point though... HRV systems are not the panacaea for leaky buildings and the resulting high heating bills.

Heating (or efficient heating) and ventilation are always in conflict with each other. The best for heating is a completely sealed building with no air changes, but this is obviously unpleasant and unhealthy. The commonly accepted compromise is 1-2 air changes per hour (compared with 5 or more for a leaky 1960s building). You can achieve this easily by sealing the building correctly, and installing standard wall vents.

HRVs give you much more sophisticated ventilation, getting rid of condensation in "wet" rooms quickly, etc, etc. However, this comes at a price... more air changes mean more air has to be heated, filters have to be replaced periodically and the pumps cost leccy to run. SOME of this cost is offset, by reusing some of the outgoing heat to heat the incoming air.

Manufacturers who claim 80-90% efficiency are talking about the efficiency of the heat exchanger, NOT of the whole system. And they are talking about fairly benign conditions.

So, maybe 90% of the heat required to bring the external air up to room temperature comes from the heat exchanger, but...
- how much heat is lost in the ducting?
- how much energy is required to run the pumps?
- how much do the filters cost?
- how efficient is the unit when the air temp is 0 degrees outside?
- how much useable heat is pumped to spare rooms that are not occupied/do not currently need heat?
- how much does it cost to run the system when the house is unoccupied?
- how many of these systems are actually installed in buildings that are properly sealed?

Anyone I've spoken to that has one of these systems has said they could never live without one, and the quality of the air is excellent, and I think this is indisputable.

However, the issue of properly sealing a house, is a *completely* seperate issue. You can have a very well sealed, efficient house without a HRV and you can have a very leaky inefficient house with one.

</2cents>

KAGY

patrido wrote:

<2cents>
I would dispute one small point though... HRV systems are not the panacaea for leaky buildings and the resulting high heating bills.

However, the issue of properly sealing a house, is a *completely* seperate issue. You can have a very well sealed, efficient house without a HRV and you can have a very leaky inefficient house with one.

</2cents>

Agreed, I assumed in the discussion that if you were considering a HRV you would be concerned with sealing the building. unfortunately I can't answer your questions re costings etc but if anyone else can i would be very interested as I'm thinking of retrofitting one in the middle future.
And if anyone has any practice sealing a leaky house I would be interested to hear about that too, though mine is tight enough, save for some obviously bad / sloppy construction techniques.

rooferPete

Hi,

I am not convinced that HRV's are good for the occupants of the house, changing air to me means fresh oxygen which is kinda vital for comfortable living and even more important where children are concerned.

The filters may control dust and odors from being transferred into different areas of the house but are they proven to prevent viruses ? the common cold being one.

As for chimney's it is possible to buy an inflateable balloon type object to block the chimney when not being used, also these systems are supposed to recover heat yet the tend to be metal ducting installed above the insulation which I think would could cause condensation on the ducting.

By all means make sure you are getting full value for the insulation you leave on site for tradesmen to install properly and use more than the regulations ask for because it will always pay for itself.

We recently had a problem reported of a stove not working properly and were asked to check the flue, we could find nothing wrong, lucky enough the stove was lighting when the Lady switched on the extractor fan over the island cooker.

The stove was going out because it was being starved of oxygen, in the USA they have been ahead of us on some of this technology and are now paying for it big time with dangerous mold (not mould) growth.

IMO, a healthy house makes for a healthy home, Patrido is in my view correct it's a system that may present a saving (or not).

I think we all should be aiming for efficiency but not a coffin.

Just my €250.00, well there is inflation to take into account

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