OK, I did a good job on the conservation side: All SIP construction, R-60 roof, EnergyStar windows, 600SF x 2 floors, etc. I left 10 100w bulbs burning all winter and when outdoor temps were zero F outdoors it was 40 degrees inside, the rest of the time it was high 40s – 60 or so depending on solar exposure and outdoor temp in a 6000 +/- degree day climate. This is in Upstate NY, 100 miles North of NYC.
It’s time for the production side: HVAC. Today elec. is $.15/kwh, oil around $4, LP around $3.50, natural gas unavailable. I don’t want a wood stove, pellets/corn are at $250/ton. There is no chimney, and there won’t be one. Direct vent is the only option.
I’m planning on an air heatpump for cooling, but the small amount of heat needed, probably 40K btu peak is giving me fits, with too many possibilities and not enough experience. House is wide-open format with two rooms: upstairs bedroom/office suite, half walls and no doors, downstairs is kitchen-DR-LR.
Hot water/radiant floor is out. I want air-to-air for compatibility with “big-window solar”. Looks like pellet stove/limited electric for backup is one way to go, and geothermal is the other. House will be occupied by soon-to-be retired couple who will travel occasionally.
What are people out there in the big world doing for houses with small heating loads? How pricey and reliable are ground source (wells looped together)? I gotta drill a water well anyway.
Thanks for sharing experiences…
Replies
10 100w bulbs burning all winter and when outdoor temps were zero F outdoors it was 40 degrees inside
The following is numbers off the top of my head, so there may be some errors.
If the extreme insulation number for lights only heating is true, you only need 1.7 kW to heat to 70F - or is that suffocation air changes? 1/4 air change for 1200 sq ft is about 1.2 kW extra needed. Total heat needed = 2.9 kW.
Average home uses about 1.8 kW 24/7 for appliances, lights, HW heat, etc. , that leaves 1.1 kW needed assuming > 50% of HW energy stay in the house.
2 people provide 300 watts of heat, that leaves 800 W of heating needed (2.8 BTUs/hr)
I'll assume your air-air AC/heat pump is a 2 ton affair, (e.g, has a reversing valve) it will provide about 8500 BTUs per hour at a COP of 1.5 at 0F outside temp. Assumed 2 T vs. your 3.5 Ton (40K BTUs per hour reference)
8500 BTUs per hour is equivalent to 2.5 kW electric strip heating, way more than enough. Backup resistance heat gives plenty of 'stay warm' margin. Even At 0 F outside, the HP would be on only about 1/3 the time if all is as well sealed and insulated as referenced; the HP will draw only about 1.6 kW. You do not need any GSHP, At 0F outside, your montly electric bill (all inclusive) would be about
(1.8kw+0.33*1.6kW)*.15*24*30 = $251. Even without added heat, the bill would be $194, for a 'heating' bill of only $57 at 0F outside.
Upstate NY avg low temp in Jan is 16F, so the $57 is probably only $40. The $40 would encompass 30*(70-16)= 1620 degree days.
COP is lots higher at higher outdoor temps, so yearly heat bill will be under $150.
To EVER reach payback at 5% interest paid on capital, your GSHP price would need to be under $3000 !!! - would have to be a total DIY job, no labor cost.
ironic88
My home is built with SIP's and ICF's as well, 5500 sq.ft. in Minnesota where we typically have the coldest temps in the nation.. You'll find the house itself stays cool during the summer with SIP's and simple window A/C Instead of putting my window A/C's in the windows though I stuck them in the wall. That way I don't lose view.. they can be up high where they do the most good and if they come out with more efficent systems it's really simple to replace. During the winter you can either plug the A/C holes with the plug you cut out or cover the A/C unit itself with an insulated box..
I did a simple staple up from the bottom. In floor radiant heat goes in really fast and is cheap.. My heat source was water heaters.. One for bath water and one for infloor radiant.. I put a wye selector in so during the really cold months I could use them both My large window areas would have been a problem except I put a simple back up forced air furnace in place with normal direct vents under the windows..
I won't need it except on really super cold days when those windows yield too much cold to be comfortable..
The in floor radiant is a simple D-I-Y job and when you only need a few vents under windows forced air isn't too difficult either.. Start at the windows and work back to the furnace, that way you only cut one duct. The size of the furnace is dramatically smaller since you only need a supliment and not enough to heat the whole house..
Edited 6/10/2008 9:11 am ET by frenchy
Tough one. Just keep a light on ... just kidding ... you did switch to CFLs didn't you?
GSHP ... that's tough, could be expensive, but relative to load, maybe not bad? System type depends on the site. You might consider thermal energy storage with a heat pump. This would require a container ... the storage medium? ... could be water, eutectic salts, river rock? ... just trying to get your creative juices thinking about options. An exterior solid fuel boiler chargiung a thermal storage mass ... could reverse for summer cooling.
Lots of options, maybe too many. Need to begin whittling down to a managable level.
sorry it took so long to post, just renoticed thread.
radiant in floor is out need air to air for big window solar.
sounds like you are building energy saving house, what would be perfect for you is solar water heater, there is an article in "build it solar" just google you'll find it, then you just have to get or make a heat exchanger, which is a bunch of tubes of hot water running on the inside of a box that you have ducted throughout the house like you would any forced air system. when the fan (which is usually a squirrel cage) is on and the hot water is circulating you got hot air.
the only energy this would require is for the circulation of hot water and the rotation of the fan, pretty minimal.