Differential Controllers -- Vendors (Solar, Oil HW)

[plantiful]

I am looking to invest some money into a solar hot water heating system.  We are currently heating our hot water with in-line hot water from an oil furnace.  It is nice not having to worry about a leaking tank, but there is a price:  temperature fluctuations in the shower.  Hot, then cool, furnace kicks in, cold, and then the water finally warms by the end of your shower.  A water tank in front would certainly buffer this, but an oil-heated tank runs about $1700.  I can ugrade to solar for another $500-800.  

Now, to link the solar heater to the furnace, I need a differential thermostat to monitor the temperatures of both and then provide power to the regular control circuit when it is really needed.  If the solar water is hot, the furnace never needs to run.  Are there any U.S. vendors that provide programmable differential thermostats, and can these be hooked up to the thermocouple that the furnace already uses for the hot water?  

[merkurmaniac]

Not what you are asking, but you could add an "on demand" or instant hot water heater at the end of the line, before your household water supply. I have started with this and intend to add a preheater later.  One Bosch aquastar model measures incoming water temps and can handle preheated water.  The brand that I bought was a Japanese one called Takagi and it measures both incoming and outgoing water temps and seeks to main a set temp of 120°F.  I am very happy with mine.  It samples the water temp 4 times persecond, I believe.  It should consume very little gas if the water is mostly preheated already.

Richard

[picmacmillan]

there is, like the previous post suggests a guy who sells an on demand water device it is very small in size i believe maybe 6"x8", and it hooks to your electrical..apparently it uses a 2 breakers but the good thing is,it doesn't use power constantly to keep the water hot for use whenever..it stated it will give enough hot water for 2 hot showers immediately.....they were about $150 u.s. and the guy was selling them on ebay....i wanted to get one but i cna't remember what i did with his ad.....pickster

[jimjjnn]

I have a Takagi on-demand water heater. Love it  !! 2 showers at same time. I keep temp set at 47 deg C. Water warm enough for hot shower without having any cold water added to it to cool it down. No reason to waste gas by adding cold water. Sunmer time we are at minimum cost per gas. Just the service charges, which are bad enough as is.4-5 people daily taking showers , including a teen-age girl that likes long showers.

Cost was 1100 dollars(US) originally. They now have newer models that are lower in price that are better. Mine produces 216 gallons of hot water an hour. We never run out. We do have a minor fluctuation when another user turns on water but it stabilizes after a couple of seconds. Not too hot or cold tho so it doesn't really matter.

 Living in a strict code area, I had tp have a licensed plumber do the install. 900 dollars (US) for a union plumber. It vents through a sidewall. The newer ones also have a fresh air vent for combustion too. It does use some electricity when on. Less than 75 watts, but only when it is heating water.On standby , it uses less than 4 watts. It does have to be reset after power outages as the computer loses temp setting. 2 seconds is all that it requires as mine has the optional thermostat like a furnace has. It is graduated in degrees celsius but no biggie as they have a temp table on the thermostat.

It's one of the best buys I have ever made. Our gas bill dropped by 40%

[monte350c]

Hi -

I'll bet you could do this without any much in the way of special controllers...

Providing the solar heat system has its own limit switches, ie shuts off if the heated water in the solar panels isn't warm enough, when there is sun, the solar loop would heat the water. If the water stays hot enough the oil burner would stay off based on its own existing controls. It doesn't have to know WHY the water is hot.

If there's no sun there will be no heat from the solar loop, water temp will drop, oil burner will turn on.

You would still have to provide suitable over-temp arrangements for the solar loop.

Ted.

[JeroenH]

Slightly offtopic, but:

I keep temp set at 47 deg C. Water warm enough for hot shower

Where I live (the Netherlands) the rules on hot water equipment dictate that minimum temperature should be 55 degrees C to avoid Legionnaire's disease.

http://en.wikipedia.org/wiki/Legionnaire's_disease

Nasty stuff like that would keep me from tinkering with tap water. Hot water for the washing machine or home heating would be no problem of course.

[fcfcfc]

Hi:

I don't know if this comes to late for you, but similar to what the last response I read was, it goes like this.

You could use one high efficiency evacuated tube panel coupled with a commodity priced 52 gallon electric heater which you would not electrically connect. You could make it a direct pump system unless you live in a very cold climate. Use one differential controller for the collector and the 52 gallon tank. You simply put the 52 gallon in front of the "in" to the hot water coil in your oil burner. If you don't already have an anti-scald valve on the output of the oil burner you should have one regardless.

And that's it. Low front end cost, simple installation, quick ROI.

.....Bill

PS: I have a schematic if you would like it....

www.fitchconsultinginfo.com