Optimum size for new home

[Little John]

Reasonable sized houses with lots of windows with big shutters to cover them on the outside when shut. In other words, when shut, reasonably well insulated, but can be opened and flood the house with fresh air. A big garden. A wood-burner for heat and water. Electric for the rest. Beyond all of the above, no need for fancy electronic control systems or fancy materials. All of these things are about trying to squeeze more from less because of coming supply constraints.

We just need fewer people, that's all.

[adam2]

A good compromise in many cases would be a relatively air tight house with 100% fresh air supply that may be heated or cooled according to need.
All windows should be openable in case of short or longer term failure of the ventilating unit, but would be best kept shut normally.

If going the "hi-tech" route I would install fresh air supply to every room except food cooking rooms and bathrooms, in these areas I would install extract only.
This would supply fresh air to all main living and sleeping areas, and "secondhand" air to food areas and bathrooms, from which it is extracted.
The mechanicly supplied fresh air should be warmed in winter either by solar thermal, or by heat recovery.

[JohnB]

Why have so many different rooms with one function? If you're in a living room, the bedrooms are empty, and vice versa. It all adds to the complexity and cost.

[ujoni08]

I don't understand why mechanical ventilation with heat recovery should allow pathogens to accumulate more than uncontrolled ventilation (AKA windows). As I understand it, the air coming in through the MVHR is the same fresh healthy air that comes in through an open window, but it goes through a series of 'baffles' first, which transfer heat from the outgoing stale air to the incoming fresh, foresty-bug air. The outgoing stale, human-bug air is kept totally separate from this incoming fresh air. Or is it something else that I haven't thought of?

I do agree with comments above about super-insulation, etc. but I also think we should be looking to use e.g. the earth under our houses as an inter-seasonal heat store (by putting heat into it during the Summer via reversible heat exchangers, and then drawing heat from it during Winter) and also using the heat from stale outgoing air to pre-warm fresh incoming air. That way we can reduce FF consumption quite markedly. Point taken about complexity versus simplicity though... Are MVHR systems likely to need a lot of maintenance? They must have something like a pump and a compressor and thermostat.. basically a fridge in reverse. Or am I talking guano?

[JohnB]

Are MVHR systems likely to need a lot of maintenance? They must have something like a pump and a compressor and thermostat.. basically a fridge in reverse. Or am I talking guano?

On page 1, Kenneal wrote:

I don't necessarily hold with the full MVHR spec required for Passivhaus because I'm a bit of a doomer, as most here will know, and I don't think that the spares will be available in the long or even medium term. I will be experimenting with a passive ventilation system with heat recovery, Ventive, in the eco hamlet that I am planning. It has no moving parts so will last indefinitely.

I haven't contacted them yet, but it looks interesting, and apparently no parts to go wrong.

[emordnilap]

Clever. Have a look at the installation pdf (watch out - over 11 megs) to get a better handle on it.

[adam2]

The degree of maintenance required depends on the type of system.

Simple heat recovery systems usually consist of a supply air fan and an extract fan, with an air to air heat exchanger between the supply air duct and the extract air duct.
The fans can fail, and do but should be easy and cheap to replace, the true doomer would keep spares.
The rest of the equipment should last indefinatly.
This simple system has the drawback that the fresh supply air will allways be cooler than the air being extracted, heat loss is much reduced, but no heat is actually added.
In most systems an additional heat source is still needed, though this will be smaller and cheaper than without heat recovery.

More complex systems use a heat pump, which adds considerably to costs and complexity. The merit of such systems is that the supply air can be heated to a higher temperature than the extract air.
The heat pump might for example cool the extracted air from 25 degrees down to 15 degrees, and heat the supply air from zero degrees to 35 degrees.
Most such systems can also cool the supply air, and dump the resultant heat into the extracted air.
Such systems are rapidly becoming the norm for large offices and are sometimes used domesticly.
If well designed they work well, but innvolve a lot of high rechnology.

Apart from cost and complexity, the main drawback of these systems is that they dont work if the internal temperature is too low, the extract air if too cold wont allow the heat pump to heat the supply air.
This can be a problem in a newly constructed building or one that has been left empty in winter.

[ujoni08]

Thanks, Adam2. Very clearly explained.

[sam_uk]

I like the look of the ventive things too. I think they are about £900/ per room. The lack of power consumption is a major plus.

I'm also interested in this specifically for bathrooms: http://www.envirovent.com/heatSava/ At around £300 it seems like it would be useful in areas that need more active humidity management. I believe they are between 5-25watts consumption.

[adam2]

Work is now substantialy complete with building finished and fitting out largely finished.
Solid fuel cooker fitted and working, heats the upstairs by a simple loop of pipe.
Heat pumps fitted and working fine.

Pv fitted and working, 24 volt battery of almost 5,000AH, center tapped to give 12 and 24 volts.
Lighting, refrigeration and many other appliances are low voltage DC.
Two inverters each of 4KW for heat pumps, washing machine, power tools and limited electric cooking.
Two Rutland wind turbines have contributed more than expected even allowing for the windy weather.

Solar hot water has not met expectations, investigation underway.

The other problem has been the unavailability of high power, high efficiency 12 or 24 volt lamps.
12 volt CFLs are readily available, but only up to 11 watts in the reputable makes.
The main living area had to be equiped with a fitting that takes 4 lamps, in order to get enough light. The single pendant lights in the food preperation area had to be fitted with vintage 3 way adapters in order to insert 3 lamps into each holder. (Now replaced with 24 volt flourescent fittings, 36 watt each)

[vtsnowedin]

Work is now substantialy complete .......

The other problem has been the unavailability of high power, high efficiency 12 or 24 volt lamps.

That is a bit odd. I would think that the Auto industry, particularly the rec. vehicle makers would have several options for Class 'A 'RVs. that were set up for 12 volts and were both efficient and tastefully done as well as being bright enough.

[featherstick]

Why have so many different rooms with one function? If you're in a living room, the bedrooms are empty, and vice versa. It all adds to the complexity and cost.

A weekend with my kids will answer that question for you.

[adam2]

Work is now substantialy complete .......

The other problem has been the unavailability of high power, high efficiency 12 or 24 volt lamps.

That is a bit odd. I would think that the Auto industry, particularly the rec. vehicle makers would have several options for Class 'A 'RVs. that were set up for 12 volts and were both efficient and tastefully done as well as being bright enough.

The main need was for relatively high output 12 or 24 volt lamps to fit standard lampholders.
Stecca and Osram both make 12 volt CFLs, but only up to 11 watts, which is a bit miserable unless a number are used.
12 volt 20 watt CFLs are sold on fleabay but turned out to be of very doubtful qaulity.
Initialy recourse was had to energy gobbling 24 volt 100 watt incandescents !

Problem solved in the main living area by use of fittings that each take 4 lamps, and in cooking area and workshop by use of 24 volt 36 watt linear fluorescents.
Bedrooms fitted with a central pendant equiped with an 11 watt CFL and a reading light over the bed with a 13 watt tube.

[kenneal - lagger]

The point is that buildings with mechanical ventilation, even when they are deemed to have adequate air volume changes, still have a different bacterial species composition to those that are naturally ventilated.

The implication (though this was not part of this research) is that the 'natural' species composition typically associated with soil and trees is healthier for us to live with than the composition dominated by species that live on our bodies, some of which are pathogenic.

If this implication is right, then it does present a real and difficult problem for the buildings industry.

The real and present difficulty is that most people like to live in a hermetically sealed box at a relatively high temperature which will not provide the conditions for the growth of forest bacteria but will provide the conditions which suit those pathogens. If you could persuade people to live at a lower temperature there would not be a problem.

You are more likely to be able to persuade people to live at the lower temperature required in a well insulated house with a controlled ventilation rate than you are in one with a howling gale blowing through. If you build an air tight house with openable windows you can seal it up on days when it is very cold and then air it out when the weather warms up. Meanwhile the MVHR or passive stack ventilation can keep the house at a reasonably healthy level of ventilation.

The problems comes with trying to convince the nutters of this world who like a howling, unhealthy gale blowing through the house and those who like to live in a hot, unhealthy fug to moderate their requirements. Both extremes are as unhealthy as each other but in opposite ways.

[woodburner]

The point is that buildings with mechanical ventilation, even when they are deemed to have adequate air volume changes, still have a different bacterial species composition to those that are naturally ventilated.

The implication (though this was not part of this research) is that the 'natural' species composition typically associated with soil and trees is healthier for us to live with than the composition dominated by species that live on our bodies, some of which are pathogenic.

If this implication is right, then it does present a real and difficult problem for the buildings industry.

The real and present difficulty is that most people like to live in a hermetically sealed box at a relatively high temperature which will not provide the conditions for the growth of forest bacteria but will provide the conditions which suit those pathogens. If you could persuade people to live at a lower temperature there would not be a problem.

You are more likely to be able to persuade people to live at the lower temperature required in a well insulated house with a controlled ventilation rate than you are in one with a howling gale blowing through. If you build an air tight house with openable windows you can seal it up on days when it is very cold and then air it out when the weather warms up. Meanwhile the MVHR or passive stack ventilation can keep the house at a reasonably healthy level of ventilation.

The problems comes with trying to convince the nutters of this world who like a howling, unhealthy gale blowing through the house and those who like to live in a hot, unhealthy fug to moderate their requirements. Both extremes are as unhealthy as each other but in opposite ways.

I am not fit, but I am healthy and suffer from few maladies. Biff's earlier post was

There was an interesting article in New Scientist last week about some research on the bacteria populations in houses. Turns out the houses with mechanical ventilation, and the Passiv House with it's MHRV system fits this bill, tend to be populated with the bugs that live on people, while houses ventilated naturally with draughty cracks of windows that open, tend to have a bacterial biodiversity associated with leaves and soil.

I don't see that your theory of controlling the ventilation with things like MHRV is doing other than the report suggests, in that it provides an environment for unhealthy bugs to live. I live in a victorian house with gappy windows. There is often a window open, but I may shut it on Thursday.