Do you live with MVHR? Opinions?

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Vortex2
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Do you live with MVHR? Opinions?

Post by Vortex2 »

Aftre years of living in draughty, freezing houses we now live in an MVHR based eco house with permanently closed triple glazed windows.

The insulation makes the place VERY quiet.

The MVHR keeps everything at a steady pleasant temperature.

We have steady hot water.

We have extensive glazing on one wall which keeps the place feeling very open and bright.

I could get to like this!

If you live with MVHR how do you find it?
raspberry-blower
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Post by raspberry-blower »

Hi Vortex

Whilst I haven't got MVHR personally you may find this useful - they had MVHR installed here:
http://www.earthwiseconstruction.co.uk/ ... kbrighton/
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools - Douglas Adams.
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adam2
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Post by adam2 »

No direct experience of domestic sized systems, though considerable experience of office block sized MVHR.

I can see the merit of domestic systems whilst times are normal, reduction in heating demand, and a continual modest fresh air supply without draughts or excessive air flow from open windows.

I would be reluctant to be reliant on such equipment in the long term due to the need for electricity and spare parts.

I hope that all your windows CAN be opened even if the intention is not to open them normally.
I would also consider a small multifuel stove to be a prudent addition, this wont be needed, and might cause overheating if used with MVHR, but is still IMHO worth installing as a standby facility for the long emergency.
On Christmas day turn off the MVHR, open the windows slightly and light the fire as an annual practice for emergency conditions.
Keep a couple of tons of coke for emergencies, the regrettable carbon emissions from use of same are of relatively little importance if the fuel is an emergency reserve, rather than your usual heat source.
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vtsnowedin
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Post by vtsnowedin »

May I ask what you have for a ventilation system and what it's capacity is in cfm?
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emordnilap
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Post by emordnilap »

A simple explanation of the principle of MVHR would be useful at this point.
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adam2
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Post by adam2 »

emordnilap wrote:A simple explanation of the principle of MVHR would be useful at this point.
Mechanical Ventilation with Heat Recovery.

Generally understood to mean a system whereby stale air is extracted from a building by a fan and extract air ducts.
A second fan supplies fresh air via a second duct system.

The heat in the extracted air is recovered via heat exchanger and used to warm the fresh air.
This is usually achieved via an air to air heat exchanger.

Heat loss and heating demand is thereby much reduced, but some heating will still be required.
On a cold day, the extracted air might be at 20 degrees, and the fresh air might be warmed to 17 or 18 degrees.

A more sophisticated system uses a heat pump to chill the outgoing air and heat the fresh air.
This can provide all or most of the heating demand under most conditions.
On a cold day the extracted air might be at 21 degrees, and might be cooled to about 10 degrees by the heat pump.
The outside air might be heated from about freezing up to about 25 degrees before being ducted into the living space.
The heat pump will have a much better COP when working with warm extracted air than with cold outside air.
This might suffice as the main heating, but has the drawback of greater cost and complexity, and energy use by the heat pump.

Neither system works well with newly built or previously unoccupied premises that are very cold inside. They work by re-use of internal heat and don't work if there is no significant heat to re use !
In such cases temporary heating from LPG or paraffin may be needed.

Most such heat pump systems are reversible and can cool the fresh air in summer, dumping the waste heat into the extract air.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
vtsnowedin
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Post by vtsnowedin »

Such a system also has to make up for all the heat lost through the walls windows and roof. Even with passivhaus levels of insulation this is considerable as occupants do keep opening doors to enter and exit. That heat can't come from the exhaust air as it is already cooled by that amount of BTUs. In milder climates it can easily be captured by a heat pump from the outside air but at -40 electric resistance elements become the way to go.
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Vortex2
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Post by Vortex2 »

We have a hybrid solution : there is a 700w electric heater in the air supply line, controlled by the system.

There is also an automatic immersion heater in the water tank section of the unit.

We use a radiant heater to give the system a hand when it's failing to get up to 20C.

Interestingly that 800 watts I assume is being (mostly) recovered by the heat exchanger.

However as noted above I assume that we will be heating the fabric of the house for days/weeks.
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