Back Up Heat Source and Boosting Loop Temps

MN Renovator · 02-07-14, 11:47 PM

The Passivhaus standard is a bit strange but keep in mind that the passivhaus standard has an OR in there.

"The specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m² (3.17 btu/h.ft² per hour)."

This allows my heat load of my 2100 sq ft house to be 6657BTUhr(my design temp is -11f or -13f depending on where I look). Now in his 1000 sq ft bungalow that would be 3170 BTUhr at design temp. A question that I've never seen the answer to is how the design load in Germany is derived. In the US, design temp is the point where it warmer than that temp 99% of the time(or colder 1% of the time depending on how you look at it). 1% of a 8760 hour year is 87.6 hours. What standard does Germany use, is it ASHRAE? Either way, I'm sure the design temps aren't far off but that's just an aside.

For my house, to get to 6657BTUhr at design temp, I need the absolute best U-value .11 windows(R9), R100 in the ceiling, R45 walls, and to not lose much through the basement. Of course passivhaus ignores the temperature that an area reaches. If my design temp was 15 degrees, I'd be okay with R35 walls, R60 ceilings, and a much more affordable U-value .2 windows (R5). Instead of going passivhaus, I'm willing to use those numbers to get to just under 10k design load. 4 inches of rigid foam makes life easier and I'm content with a heating bill consisting of about $40 of natural gas or cutting the $210 of natural gas connection fees and moving things to mini-split electric. Sure my winter months will cost more but there will be a good savings by not paying the connection fee.

Now with a GSHP, taking a look at an example manufacturer, how about the biggest one Waterfurnace. Their smallest unit isn't even offered with an ECM motor so the efficiency is a bit lower but with the low load I think it is good enough. Fans law indicates to us that lower air flow is less power needed. Their 5 series model 012 unit at 4gpm flow and 400 CFM airflow provides 14,500BTUhr cooling at 59 degrees entering water temp with 25.5EER and 12,300 heating with 50 degree entering water temp and 4.5 COP. If you've got an R30 wall, R80 attic, etc. 1000 sq ft bungalow that needs more than 12,300BTUhr heating, you need to work on the infiltration losses.

02-07-14, 11:47 PM	#25
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 940 Thanks: 41 Thanked 117 Times in 91 Posts	The Passivhaus standard is a bit strange but keep in mind that the passivhaus standard has an OR in there. "The specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m² (3.17 btu/h.ft² per hour)." This allows my heat load of my 2100 sq ft house to be 6657BTUhr(my design temp is -11f or -13f depending on where I look). Now in his 1000 sq ft bungalow that would be 3170 BTUhr at design temp. A question that I've never seen the answer to is how the design load in Germany is derived. In the US, design temp is the point where it warmer than that temp 99% of the time(or colder 1% of the time depending on how you look at it). 1% of a 8760 hour year is 87.6 hours. What standard does Germany use, is it ASHRAE? Either way, I'm sure the design temps aren't far off but that's just an aside. For my house, to get to 6657BTUhr at design temp, I need the absolute best U-value .11 windows(R9), R100 in the ceiling, R45 walls, and to not lose much through the basement. Of course passivhaus ignores the temperature that an area reaches. If my design temp was 15 degrees, I'd be okay with R35 walls, R60 ceilings, and a much more affordable U-value .2 windows (R5). Instead of going passivhaus, I'm willing to use those numbers to get to just under 10k design load. 4 inches of rigid foam makes life easier and I'm content with a heating bill consisting of about $40 of natural gas or cutting the $210 of natural gas connection fees and moving things to mini-split electric. Sure my winter months will cost more but there will be a good savings by not paying the connection fee. Now with a GSHP, taking a look at an example manufacturer, how about the biggest one Waterfurnace. Their smallest unit isn't even offered with an ECM motor so the efficiency is a bit lower but with the low load I think it is good enough. Fans law indicates to us that lower air flow is less power needed. Their 5 series model 012 unit at 4gpm flow and 400 CFM airflow provides 14,500BTUhr cooling at 59 degrees entering water temp with 25.5EER and 12,300 heating with 50 degree entering water temp and 4.5 COP. If you've got an R30 wall, R80 attic, etc. 1000 sq ft bungalow that needs more than 12,300BTUhr heating, you need to work on the infiltration losses.