Advice on ventilation ecorenovation
 

Our house has gravity ventilation, ie each room is connected to the chimney shafts through a hole in the wall. During cold days heat from the upstairs rooms escapes through one chimney shaft, while very cold air comes into the downstairs and basement though another. I've closed some of the holes, some only partially, but cold air still seeps in through windows, doors, etc. This kind of ventilation can account for up to 40% of a house's heat loss, in our case I estimate it's at least 15%-20%. To would be much more efficient to warm the incoming air with the heat that would be normally lost, so I plan to close the chimney shafts and run the air through a heat exchanger. I'm also impressed by heat pumps that use ventilation exhaust to warm hot water, like Viessmann Vitocal 160-A WWK or Stiebel Eltron WWK 300. An underground heat exchanger would further increase the efficiency of the system.

http://ecorenovator.org/forum/attach...0&d=1268507990

This set-up would be ideal, but since recuperators can have efficiencies as high as 90%, then the exhaust air may not have enough heat to be used for water heating. I read somewhere that there would only be 400-500W of usable heat in the post-exchanger exhaust. The heat pump in a water tank system uses over 400W, so it can (should) pump at least 1000-1500W of heat, much more than the exhaust air can offer. Increasing the ventilation speed will increase heating needs in the house.

So maybe I should ditch the hot water tank/heat pump combo and use a small (100-150W) heat pump to transfer heat from exhaust to fresh input air? Hot water would be an electric/solar setup, independent from ventilation.

http://ecorenovator.org/forum/attach...1&d=1268507990

But I haven't seen heat pumps rated at below 400W, so I figure I'd have to DIY it from a fridge compressor (rated at 50-250W).

What do you guys think?

You're going to need some sort of pre-heater as well. HRV's have problems with frosting up when the air outside is very cold. It can condense the water in the warm exhaust air and freeze it.

I'm hoping that a properly installed ground source heat exchanger (gshe) will use the ground's thermal mass to pre-heat the incoming air enough to always keep it above freezing, even at the end of a long winter. I have yet to read in detail about gshe's, so I may be wrong.

Ah, sorry, I was reading your diagram as if it were upside down! It makes much more sense now haha. I guess I'd aim to make the most efficient heat exchanger and forget the heat pump. Less moving parts, easier to do (IMO).

Magic Box...
 

Piwoslaw,

This is a great idea, and it has been done before. Here is a link to a discussion of such a system. Interestingly, the person who posted did not break into the refrigeration circuit, but modified the sheet metal to get the air flow he wanted.

The article also has these links to compressor-assisted HRVs

Link 1
Link 2

If you wanted to try to DIY, refrig compressors are usually lighter-duty than AC and de-humidifier compressors. I'd recommend a small de-humidifier if you can find one because the compressor is better and the electronics already have a defrost cycle built in. If you were very careful, the de-humidifier has two air-to-refrigerant exchangers and you might be able to separate them enough to get what you want with no need to break into the refrigeration circuit.



And here is an awesome link to information regarding multi-function boxes that provide:

• Air Conditoning
• Heating
• Heat (and cool) Recovery Ventilating
• De-Humidification
• Water Heating
• Utiization of Geothermal temperature differential (optional)

...all in one box!


Here's a link to one


Here's a link to another one


This one is almost a magic box


Here's a Japanese variant that went into a test house in Portland

I can't affort such a glorious 'Magic Box' but I sure am tempted to try to make one.

-AC_Hacker