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Old 11-30-11, 04:59 PM   #139
Ko_deZ
Helper EcoRenovator
 
Join Date: Jun 2011
Location: Norway
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Quote:
Originally Posted by AC_Hacker View Post
It seems like an Arduino might be suited to monitoring the sensors, but I have no idea yet how to integrate the data and act upon it effectively.
I suggest increase fan speed, or decrease fan speed to keep them both stable. Say 1% fan speed per 1% RH, and something similar for CO2. Then you use the highest of the two. I also suggest adding a "vent" button that will run the fans at 100% for 20 minutes or something like that.
Quote:
Originally Posted by AC_Hacker View Post
The single-room HRV idea seems really interesting to me from the standpoint of dealing with local concentrations of humidity, cooking odors and also CO2. It seems that if the kitchen is a source of humidity and cooking air, why purge the whole house.
You do not purge the whole house. You place one exit valve in the kitchen and in each bathroom/washing room. If you have an area with higher ceiling, you place one there too. Last, place one in the top floor as high as possible. Humidity goes up, so you need to vent from high up to get the humidity out. Input air should be in living room and bedrooms. There are different end valves for ceiling input and wall input (the wall input is the same as the output valve in both ceiling and wall). What this configuration does is that it moves air in to and out trough the ducts in both bathroom and kitchen, reducing the spread of smell and humidity. If you have single room HRV, the air will not be travelling into these rooms, thus you will allow much more of the smell and humidity to spread. Not necessarily a problem, but at the least a small inconvenience.
Quote:
Originally Posted by AC_Hacker View Post
Also, I have had my thinking aimed at sealing my house against leaks for so long, that the idea of intentionally making two holes in the wall of each room makes me uncomfortable. I mean, if there was a strong prevailing wind, which is not an unusual occurrence where I live, I think that the net result would be that there would be a mass airflow through the house, taking the heat with it.
You are very right, your indoor doors will not hold air pressure very well. A 10m/s wind does generate a very high pressure difference on different sides of the house. Before we started making our houses so air-tight the wind would blow straight trough the walls. You could use some very simple electronic properties to avoid, or at least reduce, this. If you put a flap on both input and output that the fan will blow so it opens, you could use an electro-magnet to hold it shut if it starts to get windy. Sparkfun has wind speed readers that would suit this perfectly, but it will affect the efficiency of the fans. A servo that moves something like a blinder to close the opening could be better, but not so easy to get tight. I suggest also using temperature sensors, so that you can avoid icing and automatically start cooling if it gets very warm. If you use the LM35 (iirc), you can just connect one leg to +, one via two normal diodes to -, and the last one one analog input on the arduino, and you get the temperature in steps of 1C per 10mV, or something similar with a F version. The resolution is about 0.5C, which is more than enough. I did just this for the termostat for my floor heating, and it is excellent.
Quote:
Originally Posted by AC_Hacker View Post
But I am seeing evidence, especially coming from Scandinavia, that direct-vent HRVs are receiving serious consideration.
The swedes are looking into this a lot I know, and the danes with their brick and concrete houses don't have so many other options for refitting. For the swedes, the main reason seems to be that their normal heat recovery the last years seems to be having air-vents in the bedrooms, and then a suction system with a heat pump, pulling air in trough the holes in the walls and out from the kitchen and bathrooms, and then recovering energy from the outgoing air. There are a few disadvantages to this, one major one is icing on the cold side of the heat pump which significantly reduce the efficiency, another is the cold area that you get around the vents, when closed there will be dew and other nasties. Also, with very high dT the heat pump cannot manage to exploit the outgoing air energy very well. To "fix" this problem i houses that are already built, single room HRV is the easiest way to accomplish an improvement. Also, Sweden is not very windy. Take Norway as the opposite. We have 10m/s regularly, so this single room system would not work at all. Danes have it worse with regards to wind, so this will be very interesting to see how plays out.
Quote:
Originally Posted by AC_Hacker View Post
So far, the passive house approach uses a central HRV. I don't know yet if one approach is ultimately more efficient than the other.
There must be comparisons done to determine this, but in the long term I do believe that total cost of ownership will be significantly less with a central system. Easy to maintain, efficient, and expensive components will make the lifetime a lot higher. Production pollution also goes into the calculation, and something that last longer is usually more environmentally friendly. Also, if something more efficient comes along, you can always change a central unit, not so easy with 10 singe room ones.

I do think this is a very interesting project, even though I have very little faith in it ending up as a cost-efficient solution. If you need any help with the arduino, let me know.

Btw, pretty much all passive houses that where built 15 years ago (as experiments), seems to be getting humidity damage and rot. I talked with a few people that helped putting those houses together. Not much has changed in the building process. Some materials have gotten better, and the humidity block quality and awareness has improved but that is about it. I am dreading how it will end with my house after the next 20 years.
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