Replies

1. 
   Jay20 | Mar 06, 2009 04:55am | #1

   I have one of those systems. In the summer I turn it on at night and off during the day. In the winter I turn it off when the outside temperature is below 32 degrees. Spring and fall on all the time. 

2. 
   NRTRob | Mar 06, 2009 06:13am | #2

   use a good HRV, design with low flow ports, maybe even use a "blending" ventilator.

   turning off your ventilator when it's cold... in an area that gets to -20... isn't very feasible. That's when you need it most (you're all buttoned up in there).

   -------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com
1. 
   KenLewie | Mar 06, 2009 06:23pm | #3

   Thanks for the info!  I have also heard of water to air recovery systems that use the hydronic system to add supplemental heat to the incoming air.  Do you know of such a thing?  I agree that the winter is when you need it the most especially to dump excess moisture from inside the house.  I plan on having an indoor green house as well so moisture will be a factor.

1. 
   NRTRob | Mar 06, 2009 06:30pm | #4

   there are lots of hydronic air handlers that could be used. a sensor in the duct to fire if you are below a minimum temperature would do the trick. However if you are very cold, the fan unit's defrost may be challenged. be sure to choose a unit rated for such cold weather.-------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com

2. 
   Clewless1 | Mar 08, 2009 06:33am | #8

   Theoretically you could ad a hot water coil to the incoming air stream to limit how cold it would allow the air to be. But this may be an energy 'problem'. The coil could be controlled by a duct thermostat set at e.g. 50 deg or whatever (that's pretty cold).

   What air change rate is the HRV giving you (air changes per hour)? If it is above say 0.35, then you want to take care dumping additional air into it.

   The manufacturer may have something to say about this, too. Frankly I've never heard of any issues like this w/ HRVs ... even installed in Alaska.

3. 
   rdesigns | Mar 06, 2009 06:47pm | #5

   If you worry about -20 temps, just turn it off for those few hours of the winter if you find it uncomfortable. However, my guess, based on years of reviewing heat load calculations and heating designs, as well as actually inspecting the installed systems, is that you will  find that the operation of the HRV (heat recovery ventilator) will not decrease comfort.

   The HRV distributes its tempered air, and the hydronic system will respond to this increased heat load just the same as it will to the loss thru, say, a large window.

   For example, a typical 4' x 5' window will lose about 700 BTU's/hr at -20. The distributed, tempered air from the HRV will need about 45 BTU's/CFM to re-heat the incoming air. This means that the window will need the equivalent of about 15 CFM constant airflow from the HRV.

   I would highly recommend the HRV on the basis that, even if there are times when you shut it off to maintain comfort, the big picture will be that indoor air quality will be greatly improved for the overwhelming majority of the year.

   If I knew your location, I could give you the winter design temp. for it. A 99% winter design temp. of, say, -6, means that, for decades of recording, for only 1% of the number of hours of the year does the temp. fall lower than -6.

1. 
   KenLewie | Mar 06, 2009 07:18pm | #6

   First I want to thank everyone for their help.  What a valuable resource this site and it's members are...

   I will be building my parents their retirement home (they currently live in an RV all over the US) in Deer River, Minnesota, which is near Grand Rapids.  I'm designing and building it for free as cost is an issue, and well they are my parents.  I feel fortunate to get the opportunity.  It will be a super insulated cabin like home (R30 walls, R80 ceiling) and mostly heated with solar hot water with supplemental heat from a high efficiency hot water heater.  Sand bed with stained concrete floors and a green house as my mom loves to grow food.  It's a real challenge of my engineering, construction, electrician and plumbing skills to integrate all of the systems involved and I'm finding out all kinds of things I don't know every day.

   Thanks again!

   Ken 

1. 
   rdesigns | Mar 06, 2009 11:51pm | #7

   Deer River is beween Bemidji (-26) and Hibbing (-20), so it appears that your -20 estimate is valid. (Grand Rapids is not listed in ACCA Manual J.)

   Since you'll be building new rather than retrofitting the heat system, you will have the advantage of being able to size your heating system based on an accurate heat load calculation.

   The load calc will, of course, need to take all the major factors into account--like the load imposed by the HRV, window areas and window u-factors, super insulation, and (probably) super air sealing. You will likely be surprized at what a small heat load there will be. I'm guessing that, if the house is around 1500 sq. ft., it might come in at around 60,000 BTU's or less. The wild card will be the greenhouse--big solar gains at times, but huge losses at night.

   Sounds like a very interesting and challenging project. Best of luck.