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stmbtwle

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Reply with quote  #21 
I think I would go ahead and build the DHW system. You're going to want it anyway, but it's my feeling that DHW and space heating are not that compatible, as the desired temps, pressures, and volumes are different. Others may have a solution.

Do you have an electric or gas water heater and if so how big is it? You may be able to integrate your solar DHW system into it, and you'll always have the electric or gas for backup.

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Willie, Tampa Bay

gbwillson

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Reply with quote  #22 
Jim-

Looking at your floor plan I was wondering:

-Are all three bedrooms in use?
-In which room is the most time spent?
-Which room seems the coldest?


Greg in MN

Jim

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Reply with quote  #23 
Willie - We have a 45 gallon propane water heater. Plans are to run a pex heat exchanger coil through the drums before it goes into the water heater. The drums are unpressurized, but the pex coil will have full system pressure. The water in the drums will be circulated through the roof-mounted collectors with a variable speed temperature sensing pump. They will drain back into the drums when the pump shuts off.

 Another pump will circulate this same water through the floor loops once that system is functioning. I want the air heating system to be a temporary system until I get floor heat into all the rooms, which will take a number of years at my current pace. You're right, for a hot water radiator you need some pretty hot water, but for in-floor heat, I think anything from 80 to 140 degrees should do the job. I just need to make sure I have enough heat exchanger capacity to warm up the domestic hot water to about 110 or so on its way through the coil in the drums. 

Sound about right to you or am I missing something in my thinking here?

Greg, bedrooms #1 and #3 are currently in use. #2 will be used just as soon as I pour a concrete floor and install some kind of floor covering. The wooden floor in that room had rotted out due to a water leak in the adjoining bathroom wall.

We spend most of our time in the dining room and living room. When the wood stove is going, the kitchen and bedrooms are the coldest rooms. The bedrooms warm fairly quickly with the morning sun, but the kitchen stays chilly until afternoon when the sun comes through the west-facing window.

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Jim in Chihuahua, Mexico
stmbtwle

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Reply with quote  #24 
Sounds like a pretty good plan to me! I had thought you might be able to go with an open system and dispense with the heat exchanger, but it might be a bit small for you, and doesn't work with drainback.

I'm not that familiar with the HEX style of setup though, so I'll let those with more experience advise.

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #25 
Engineer your radiant heat floor to operate at the same temperature range as your DHW. Do that and you can simplify the system quite a bit. 




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Rick H Parker
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stmbtwle

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Reply with quote  #26 
How do you propose to do that?... my solar DHW operates at 150-170F.

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #27 
You don't need to run DHW that high. Most people don't because, 150 -170F is hot enough to do third degree burns in 0.25 second, it takes a human at least 0.7 seconds to react. There is the option of doing more storage, lower temperatures. Besides the objective of the game is not to get all you can get, the rational objective is to get want one needs and avoid things like a trip to the ER.
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Rick H Parker
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stmbtwle

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Reply with quote  #28 
Rick I run it that high because I get more heat storage in a given volume (with a woman in the house there is never enough), I have a mixing valve at the tank output to reduce it.

A radiant floor runs at maybe 85F or even less. I don't think many folks would like their showers at that temperature. It is a good way to conserve water though. Showers tend to be very short! [biggrin]

So, how do you propose to do what you suggested? I think attempting to do so would make the system more complicated, not simpler.

Jim you mentioned the idea of a radiator and fan but it was ugly and noisy. Admittedly auto fans are noisy AND they are 12v. One could replace the auto fan with a household one which would be much quieter and put the whole thing in a cabinet for appearance. Mine resembles an end table. It would also be more compatible with DHW temperatures.

A thought on collector placement: A collector against the side of the house actually BLOCKS the heat that you would normally receive through the wall. Setting it a few feet away would avoid this.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Gordy

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Reply with quote  #29 
Willie,

If Jim were to have a storage tank and run it at high temp's like you do, He could use 2 tempering valve's one for DHW and one for the radiant heat to keep the floors from getting to hot. Looking at the sketch of the house, I'm wondering how many zones do you think Jim will need to plumb in for the radiant heat? To keep one room from getting too warm while trying to get other rooms up to temp.

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Gordy,
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Rick H Parker

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Reply with quote  #30 
"A radiant floor runs at maybe 85F or even less."

85°F is the most common floor operating temperature but that is floor temperature not water temperature. The water supply for that 85°F floor, ranges from 85-140 °F depending on the design of the floor.

115°F is the most common water temperature for Radiant Heat Floors, for the same reason it is the most common temperature for DHW tanks, 115°F is the maximum safe temperature. Anything higher then 115 °F runs the risk of burns. 

If one sets the tank  temperature for 115°F and designs the floor to operate on water temperatures of 85-115 °F, one can use the 115 °F for both space heating and DHW without conditioning. Some people have gone this route because 115°F is safe around kids and adults that are a little absent minded. The trade off is you do need a bigger tank then you would if you run higher tank temperatures but, you get the peace of mind knowing that your not putting what really matters at risk ... which includes your own hide ... literally.


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Rick H Parker
Kansas, USA
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