"Efficient" use of solar for home heating and car charging
mtvhike
5 years ago
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Comments (43)
Ron Natalie
5 years agokevinande
5 years agoRelated Discussions
Energy Efficient + passive solar plans: comparision
Comments (24)I'm located in a hot Southern climate. We're technically north of Atlanta in latitude, but much flatter in altitude which can make a big difference. Someone south of Atlanta is likely to experience similar weather. I have friends in Warner Robbins, and our summer weather is usually within a few degrees of each other. Delta heat and humidity is brutal. We get MUCH hotter and humid springs and falls than most realize. And "humidity season" is about 10 months long. The Gulf is always swirling up massive amounts of moisture into the region. It's basically summer from April til October. Heating season is only 3-4 months long here while cooling season can run 8-10 months. There are months that overlap. Hot in the day and cool at night. It's not so much the temperature in those overlap months as it is the humidity. 81 degrees and 95% humidity is pretty darn clammy and miserable and so needs the AC to dehumidify the air. Same with 55 degrees and 90% humidity. It feels colder than it actually is because of the humidity and putting on a sweater only helps marginally. Gotta run the heat a bit to make the temp more comfortable. There are about three weeks in fall and three weeks in spring when you can actually open the windows and not suffer due to letting the humidity into the house. Planning for solar heat gain in the winter is practically ludicrous with those conditions. It's not that darn cold to begin with! Add in a bit of low sun solar gain to your average 40-50 degree winter high temperature and the house will get to 80 in no time. My neighbor's attached Southern facing un-HVAC'd sunroom regularly gets to 95 degrees on a sunny December day. In summer, even with decent overhangs, it's 130 in there by noon. Try to work with that for your home's cooling load! This is why I stated that solar planning for the South is more about minimizing the solar gain rather than trying to harness it for the brief heating period that happens. Your major energy dollars spent here are in cooling. Minimizing loads to the cooling system with the home's design is what pays off here---IF, as David says, the homeowner has the luxury of enough room to accomplish that. 95% of those building will do so on lots too small to do much more than trying to get the right windows for those Southern facing heat gainers....See Moresolar water heating and radiant heating
Comments (10)Hi gary - Several of the outfits installing solar water heating systems around here have told me that the cost of installing a system that also uses solar heated water in a radiant heat system is too high to be viable; i.e. normal solar hot water systems won't produce enough hot water for radiant heating, especially at night, so that you'd need to quadruple the collector area and storage capacity to run both systems. One guy told me that even if I tried to minimize my usage thru efficient zoning, the cost of the equipment is so muich greater that I'd still be better off reinstalling my forced air system run on natural gas. Any ideas?...See MoreHeat pump quotes? (aka like buying a new car)
Comments (3)First: I'd want to dig into the assumptions, etc. on the heat load calculations to explain the different size systems. That seems like the obvious first step. Second: I would take this opportunity to consider fixing some of the "character" of the house. Can you put the difference in the cost of these two systems into insulation, air sealing, etc. and end up with better comfort and lower energy bills? I say that as someone who pays a little over $400 a year for natural gas (heat, hot water, range and dryer) in central Indiana where it gets pretty darn cold in the winter. I have done that while maintaining all of the historic character of the 1924 bungalow. You have an energy audit. If it was done well it should provide a road map for where to invest for energy savings. If it was done poorly, it will be standard items without much application to your house....See MoreUsing attic heat to help heat house
Comments (10)This is a very old thread, but in case anyone sees it, here is my solution to this free heat opportunity: After air sealing and insulating my 530 ft condo, I continued to be irked by times in the heating season when the attic would reach 80-90deg, while the apartment was at 65. I finally ran some back-of-napkin numbers that showed that an ERV could be used to efficiently transfer attic heat into the conditioned space. So I bit the bullet and gave it a try. I installed a RenewAire EV Premium L, (largest most efficient core) and ducted it so that the attic air and the conditioned air run separately thru the ERV. Basically, the ERV pulls room air up, heats it with warm attic air, and returns it to the room. MERV 13 filters are installed in both streams, and the attic insulation is covered with plywood/plastic which prevents it from kicking up dust. The ERV is controlled by two thermostatic switches in series, so that it comes on whenever the room is below 72, and the attic is above 72. In practice, this results in an starting temp differential of about 5 degrees minimum, since I let the apartment cool to 67 overnight. That differential quickly climbs as the sun shines. Right now, for instance, at 1pm on a partly cloudy day, outdoor temp 67, attic temp 88, the system is intaking room air at 69 and returning it at 81, at a rate somewhere around 280 CFM. That comes to about 2400Btu/hr, and a “COP” of 4+, given a fan consumption of 170W. In the peak of a sunny day like yesterday, when the attic got up to 95, theoretical yield could be 5300Btu/hr, and “COP” close to 9. This sometimes won’t be a sufficient heat source. But for the shoulder seasons in this temperate sunny climate, in a small well-insulated/sealed space, I’m guessing it will be all that is necessary. In fact, my “primary” heat source may become the supplemental one. I’m not sure how scalable this idea is, but for older buildings with an accessible clean attic and a well insulated attic floor, it seems possibly worth considering. Obviously it is not cost efficient at today’s energy prices. But it is extremely energy efficient, and taking a longer view of the future costs of GHG emissions, it seems an interesting way to partly solarize an older building. Based on my temp records, I think it will also be able do some cooling at night in the summer. Total materials were around $2500, plus my labor....See Moremtvhike
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