Eco spherical objects, or...

[Flyfisher]

Very true, and I guess good insulation would certainly reduce the heat loss from the fabric of the building, but the walls, floors and ceilings are fixed items and once they are heated they will surely only lose heat relatively slowly (insulated or not) compared with changing all the internal air every 10-20 minutes.

Look at it another way; imagine a house with a heating system designed to maintain an internal temperature of 20C and which has been running for a week or so, so all the walls etc are up to the same temp (the inside faces anyway). Imagine the house has no ventilation. Switch the heating system off and imagine how quickly (slowly?) the internal temperature drops to the outside temp of, say, 5C.

OK, now do the same but in a house with ventilation that is changing the air, say, 4 times per hour. Switch off the heating and within 15 mins the ventilation factor will have replaced all the internal 20C air with external 5C air.

So, ventilation alone will reduce the internal air temp of the house fro 20C to 5C within 15 mins whereas 'normal' thermal losses will cause it to reduce to 5C within . . . . what??? I don't know the answer, and it will certainly depend on the quality of the insulation, but I bet it would be a lot longer than 15 minutes.

If this is correct then surely ventilation must be a bigger factor than insulation when it comes to heat loss from a house? And if it's not correct, where am I going wrong?

 

[chuckey]

I have an ancient (1970s) central heating guide in front of me which unfortunatley is all is BTUs- conversion later. heat losses from dining room =4,506(fabric) + 1,104(air change= 1 1/2 per hour). Bedroom = 2,120 (fabric) + 828 (air change). These figures are based on uninsulated 11" cavity walls and 1" glass fibre in loft, single glazed windows. Figures in watts(X .293) = 1300, 322, 621, 248.
So it can be seen even with rubbish insulation, the heat losses associated with 1 1/2 air changes/ hour are 25 - 40% of the fabric losses. I have re-calculated the lounge with "good" insulation, giving me a fabric loss of 2390. The air change loss is an added 1100/2400 = 45%! I would think that the heat loss for an "eco" house would be even lower, so the losses due to the air changes are extremely importent.
Frank

 

[Flyfisher]

Interesting figures - thanks for that! I stand corrected about the heat losses through the fabric of the building being greater than through ventilation, historically at least - although I'm still surprised.

However, the "good" insulation figures do suggest that we're starting to get into the area of diminishing returns on insulation investment and that ventilation is rapidly becoming the dominant factor. And with good ventilation being a health issue I wonder how long it will be before heat exchangers become the 'next big thing'?

 

[chuckey]

I have kept an interest in MV(mechanical ventilation) with heat exchangers ever since as a teenager, I saw the Philips heat wheel on Tomorrows World. It was further sharpened when some friends of ours, who had a hot air central heating system, moved. I had seen their system which was based on a 4' square brick box in the centre of the house. They had complained that all the plaster was cracking where ever a ceiling or wall touched this box. When they moved, they removed their junk from the bottom of this brick box/flue, only to discover a VERY blocked air filter!!
The only way MV can be used is if the house is designed around it or all the internal doors are left open. There are also problems associated with fan noise and dust patterning around inlets/outlets.
Let me know when you have solved these, because then I could be interested in such as system.
Frank

 

[Aidan]

The only way MV can be used is if the house is designed around it or all the internal doors are left open. There are also problems associated with fan noise and dust patterning around inlets/outlets.
Let me know when you have solved these, because then I could be interested in such as system.

They have been solved. It was never an inherent system problem, but a quality problem.

UK domestic warm air heating systems were mostly fitted as a cost saving measure on new-build houses in the '70s. They gave ventilation systems a bad name which still persists, the building services equivalent of the Skoda jokes. You can't really make a valid comparison between a bargain-basement heating system and a ventilation system, which is only intended to ventilate and maintain the indoor air quality.

Air isn't an efficient medium for shifting heat (or cooling) around; ducts are big. The usual approach is to use water for heating or cooling and minimize the size of the fresh air ducts by limiting it's use to ventilation, rather than heating &/or cooling. A filtered and tempered air supply to the main hall of a house will find it's way into all the rooms. the internal doors aren't draught-proofed. The air is clean and the deposition of airborne dust is hugely reduced. The savings on cleaning costs can be significant.

Heat recovery by thermal wheels, run-around coils and plate heat exchangers are an unavoidable fact of life in commercial buildings; I work on sites that have all three. They have already started to appear in high-end domestic installations. If you happen to live in a Building Regulations approved sealed-box, then much of the traditional infiltration has been sealed. You'll need ventilation or you'll need a doctor.

Have a Google for IAQ and the US-made Lifebreath ventilation system.