Quote:
Originally Posted by Drake
I'm not arguing that air quality is unimportant. But most government or manufactures standards lean way to worst case and error on the side of profit over savings. I like the theory of HRV but the real ones I've seen operating here in MN have frosted to uselessness when needed most and have have not made it half thru their spec'ed life without severe corrosion. Most ness systems that include pretempering incoming air have not been operation long enough to judge except that they control frosting. These add-on systems are mechanically elaborate and need to be done at construction time to be at all cost effective. Which leaves out a build and test how tight it is approach. I'm not seeing the real positive results that passive solar design, super insulating, building smaller(better use of space), LED lighting(not CFL's), PV generation, radiant heating, energy/water saving appl, real "green"/recycling lifestyle(less waste) are showing. I'm not convinced that the current HRV's are the best or only answer to fresh air. No offense to anyone. I am following the DIY HRV thread.
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You are correct that HRV's are not the only answer to fresh air. My energy auditor suggested using exhaust only ventilation and replacing the air intake that was plumbed directly into the furnace air return with a PVC pipe that runs towards the ground and then has an up-bend to stop convective air flow. He told me the same disadvantages about heat exchanger frosting and high unit cost just like you did. With the air intake setup, my natural vented furnace and water heater get their combustion air and the exhaust ventilation system would be able to get the intake air that it needs to actually ventilate the house.
The cheap and most electrically efficient option to this is by getting an energy star bath fan that is next to silent and also has the option for continuous airflow. I found the Samsung Whispergreen fan to be a great choice, one of the most efficient fans. It actually has a selector where you can choose the precise amount of airflow and it adjusts how much power to apply to the motor so that if there is negative pressure in the house or if its pushing against excess duct pressure that it will deliver the CFM that you set. Of course you need to use the ductwork size that they require and install it correctly to get that airflow.
Every HRV that I see seems to be massively expensive and pushes enough airflow for a house of 10 people. It's supposed to be about 15CFM per person with one of these fans you can adjust that airflow, with an oversized HRV you are pushing more air and using more power than you need to and since its exchanging that much air, the inefficiency of heat transfer might leave you worse off than adjusting for the exact level of airflow you really need and having no heat exchanger.
I think this system works great in the winter because you want some negative pressure on the house and the exhaust fan will ensure nothing goes positive and pushes the inside high dew point air through your insulation between you and the outside. In the summer though, it brings in high dewpoint air, in MN that air is higher dewpoint than basement temperatures or even most inside temperatures meaning that it might be a better idea to plumb the outside air into the return again and shut off the exhaust ventilator instead of allowing your intake to pull high humidity air directly into the basement.