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holding tanks
I've got an idea and want to see how it sounds. First, I seem to have a serious case of distraction this morning. I did proof read my other posts and still butchered a bunch of grammar. Sorry. My spell checker just informed me that I had misspelled ‘grammar’ as well. Tough morning!
The plumbing question is whether anybody has heard of a holding tank installed in the feed line to a hot water heater. The idea is to save electricity (in my case) by allowing well water to warm up in the house before if goes to the water heater. Some friends thought their oil water heater was coming on about every time hot water was used, and a holding tank was a plumber's solution. They say it noticeably cut their oil bills.
However, I'm not sure how efficient heat transfer from a conventional tank directly to air would be. I have looked around the net and found various specific heat exchangers designed for flowing water, which are also very expensive. I've been wondering if a set of 1" thin walled copper pipes with air space around them and standing vertically might work better. I figured that 6' of 1" pipe holds about a gallon. However, I'm not sure if a base and top for such a thing is available, and I'm not sure how to go about constructing one. It would end up weighing quite a bit, and depending on solder joints doesn’t seem a good idea.
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holding tanks
I have no solar, active heat exchange or wood furnaces in use. I've looked a bit and thought about a combination of solar and heat recovery from waste water. The equipment to do it seems pretty expensive and I wonder how long it would take to get the investment back. Of course our electrical rates are exploding, so maybe the answer is 'pretty quick.'
What's in my mind is a simple passive system. Get enough water in the basement and it would stay around long enough to warm up before triggering the electric heater. True enough that the basement would be cooler, but I'd just as soon it was for most of the year anyway. It also probably continues to get some ground heat throughout the winter. The house is heated by oil. At the moment it is cheaper than electricity by quite a bit, so I wouldn't mind if the furnace came on more often if it was keeping the electric water heater off.
However, maybe this 'do it yourself energy efficiency' isn't all that practical. Maybe Cutter's comment about a new water heater is the way to go. At the moment, I have a 'nothing special' heater wrapped with 6" fiberglass bats and covered with vapour barrier. It should at least store heat fairly efficiently. I guess I could put a loop in the output pipe. The idea is that hot water rises, so it comes up the output pipe and continues along horizontal runs until it cools. A loop in the vertical output pipe forces water flow back down and contains circulation of the hot water. I did that in another house, but it’s difficult to tell how much difference it made.
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holding tanks
Thanks for the comments. There's a couple people around here who have wood furnace boilers that heat both the house and provide hot water. That's probably similar to the Alaska rigs. I've heard some pretty good things about them. I've also heard that wood furnaces are real wood burners compared to modern wood stoves. Unfortunately, there's nothing to work with, because we've got a typical oil burner forced air system.
Yep, the connection between basement and ground water temperatures is one I wouldn't have thought of. Perhaps I should have since I had an experience at my father's place in Lake Havasu City, AZ. The city water gets so hot just flowing through the system during the summer that many people turn off their water heaters and keep a jug of drinking water in the fridge. Nobody told me, and I took a somewhat extended shower, and spent most of the time trying to adjust the water.
A lot to be said for the idea of ground heat. I do think our basement gains heat from the outside during the summer and the furnace during the winter. At least we lightly insulated the pressure tank and some of the inside pipes to reduce condensation during the summer. Sort of ironic now because the condensation cure adds to the costs of hot water.
Like Murf says, if I cost anything that will make a significant difference out, I may find very long payback times. But then, it's a little hard to forecast future electric and oil rates. Don't know, but the deep well water is really quite cold here, and our friends thought a holding tank made a difference for them. However, their problem may be more related to the particular oil water heater. The problem was that it came on frequently after using only small amounts of water. Maybe the thermostat is located close to the water intake. I don't know how much heat goes up the chimney after each burn on a water heater.
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Mostly I'm just starting to react to rapid increases in electrical rates by thinking of ways to improve efficiency. Things work OK and there's enough hot water. We keep it not especially hot, and with the extra fiber glass bats around the tank we can still turn off the heater for several days and come back to a hot shower.
I think my alternatives are: a better heater; different fuel; or waste heat recovery. I think of the original passive holding tank idea as one that would take extra heat out of the basement mostly generated by solar load or oil furnace operation. It's mostly an alternative fuel idea.
A coil around the furnace probably is a more active version of the alternative fuel idea. It would be tempting to use the flue pipe, but our medium efficiency furnace already takes enough energy out the flue gases that the top of the chimney builds up frost during very cold weather. That's a problem in it's own right.
A wood fired supplement seems like a pretty good idea, and wood can be cheap here. Outdoor wood furnaces are expensive but insurance companies like them. My brother in law recently installed a second wood stove. His insurance company has a list of approved stoves and wanted to inspect the installation themselves. Our own stove bit the dust when we discovered the chimney had to be replaced. The cost of running a new outside chimney from the basement to above the roofline wasn't a pretty penny, and stoves in basements don’t work that well anyway.
I wonder if Sedora stove is what some friends bought a few years ago. He described the stove as designed so it re-burns flue gases. Whether its the same design or not, he really likes the stove. I don't know how the addition of heat exchangers to do something like heat water might effect the efficiency of these fancy stoves.
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holding tanks
I did find a commercial heat exchange product for shower drains a few years ago. I think it's is called GFX something or another. I checked my bookmark but the page isn't on the net any longer.
As I recall, the product needs a minimum 5' vertical drop between the shower and drain. The unit appeared to be a fairly large diameter vertical copper pipe with standard water pipe coiled along its length. Info on the site said that efficiency of the unit is due to the fact that waste water going down the vertical will swirl around the inside surface thus improving the heat exchange. There also was an explanation that the unit is more efficient if it's installed in the main water feed rather than the water heater feed line. There was an explanation, but I never understood the logic.
I never became too interested in the product because our shower is shower and water heater are in a shallow part of the basement where there isn't 5' clearance above the drain. I also figured that I'd have to talk my wife into taking showers rather than baths for the idea to be worthwhile. I believe I'd rather pay the electrical bills.
I also thought about holding tanks for gray-water and active exchangers but I never got past the cost of the equipment.
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