Monday, November 22, 2010
The Hydronic Heat
Here's the entire hydronic system.
Behind the recycled doors are the demand hot water heater and the potable water manifold. Cold water comes up through a pressure regulator and is distributed to the various fixtures. Some continues up to the demand hot water heater and then back down to the hot side of the manifold and out to the fixtures. What isn't shown is that the pipes to and from the demand hot water heater have Ts in them that allow hot water to be circulated to the hydronic system. Those pipes come out of the wall right in the middle of the picture with hot on the bottom and "cold" (return from the heat exchanger) on top.
Here's the guts of the system. When the thermostat demands heat, both pumps are activated. The brown pump in the lower center of the picture creates a demand on the demand hot water heater and 140 degree water is pumped in to the heat exchanger at the top center of the photo. The red pump on the right pumps water through the heat exchanger and that water is sent to the hot manifold, circulated though the floor, returns to the cold manifold, and then back to the heat exchanger.
On the wall above the brown pump and to the left of the heat exchanger is the controls for the whole house Energy Recovery Ventalation system. The ERV is on a timer that runs it several hours per day, or I can use a manual override. It is also connected with the ducting from the zero clearance fireplace. If I want the entire house to be the same temperature (not usually necessary), I can turn the ERV on manually. It actually is most useful in the summer, when upstairs temperatures can get to 80 degrees. The ERV can mix the cooler downstairs air with the upstairs air and keep things in the mid 70s when outside temps go above 90. 
Because the red "floor" pump on the left flows 30% more water than the brown "heater" pump on the lower right, the 140 degree water from the demand hot water heater only creates 110 degree floor water through the heat exchanger. In the picture, the water has been circulating for some time, and it is going out at 110 and returning through the slab at 90 degrees. That doesn't mean that the slab is 90 degrees. Heating the 90 degree water back to 140 in the demand heater only uses 1/3 of the demand heater's capacity, so there's plenty of capacity left for the washing machine, shower, etc., if that is used when the floor is heating.
I was surprised to find out that a demand for hot water at any of the household fixtures reduces the efficiency of the brown pump to the point where it barely sends warm water though (it effectively increases the "head" on the pump). What that means is that household fixtures have priority. If you're in the shower and the heat comes on, you won't notice. Basically, the hydronic heat won't effectively be on until the shower is finished. Not a big deal because my house temps only raise and lower about a degree per hour.
The manifold has control valves for the flow through each of the three 250' circuit loops, plus the manifold valves, the pump valves, and the pumps themselves can be adjusted for proper heat exchange and distribution. There were enough variables in the system such that I could fine tune it without any additional complex zone valves, bypass valves, etc. The system is very simple. (1/4/14 note: it has now been more than 3 years without an adjustment or any maintenance).
There is an expansion tank. The pex tubes coming through the wall run up into the attic. It's a project that I may or may not complete. So far, I'm happy with what I have, but the next picture explains the possible future use of this pex. Plus, I have to get the system strapped in better. I just pieced it together sufficient to get my certificate of occupancy.
In the attic is a water to air heat exchanger that can be connected to the pex tubing at the manifold. When the heat and the ERV are on at the same time, I can send 110 degree water up to the heat exchanger and then distribute warm air thoughout the house via the ERV ducting. In a similar manner, if it gets hot during the summer, I can send slab temperature water (65-68 degrees) though the heat exchanger and distribute cooler air through the house. The slab will gain some heat during a hot day, but it would distribute it overnight to the house. Haven't seen the need for the system yet. (1/4/14 note: Still haven't needed the system, although with climate change it might be nice to take late summer attic heat and store it in the slab).
# posted by gnome-honey @ 12:59 PM 
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That's a great detailed writeup. Thank you for giving this system a post of its own.
I like the philosophy you seem to be using for each component of your house: research, plan, buy quality new and used materials, and adapt the plan when necessary. Overall, be willing to put time and money in up front to reduce the amount of time and money needed for future comfort.
It's inspiring, not only because you're doing it, but because you're sharing the details. I hope you'll continue to share how each investment is working out as the years go by.
pc
I like the philosophy you seem to be using for each component of your house: research, plan, buy quality new and used materials, and adapt the plan when necessary. Overall, be willing to put time and money in up front to reduce the amount of time and money needed for future comfort.
It's inspiring, not only because you're doing it, but because you're sharing the details. I hope you'll continue to share how each investment is working out as the years go by.
pc
# posted by 
: 6:37 AM
: 6:37 AM
The under-slab part of the construction is back in the archives at July of 2008. Like most people who have never been around hydronic heat, I thought that laying out the tubing was the "guts" of the system. Nope, it's the pump/manifold calculations. The tubing was simple, although I would change two things.
First, based on what I'd read, I didn't put any tubing under the sofa and kitchen cabinet areas. I'd still leave it out from under the lower cabinets/fridge (warming under the fridge is a real waste and cabinets can "overheat" to 80-85 degrees and reduce the shelf life of stored food. Best to let both of those areas stay as cool as possible). But area for the sofa wasn't worth messing with and it will be noticable if the couch is ever moved to another location (not likely).
Second, I would have placed additional PEX tubing in the areas that I knew could use some additional help. I already did that at the base of the stairway. I knew that cold air would be coming down those stairs, plus, it's right by an exterior door (which is probably R5 if the weatherstripping is perfect). The extra PEX at the bottom of the stairs is just noticable enough if you're in stocking feet and going upstairs. But even with that, there is a gentle flow of cooler air that enters the living room. An extra bit of PEX there and under each of the larger windows probably would have been a good idea for those stretches where we have several days below freezing.
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First, based on what I'd read, I didn't put any tubing under the sofa and kitchen cabinet areas. I'd still leave it out from under the lower cabinets/fridge (warming under the fridge is a real waste and cabinets can "overheat" to 80-85 degrees and reduce the shelf life of stored food. Best to let both of those areas stay as cool as possible). But area for the sofa wasn't worth messing with and it will be noticable if the couch is ever moved to another location (not likely).
Second, I would have placed additional PEX tubing in the areas that I knew could use some additional help. I already did that at the base of the stairway. I knew that cold air would be coming down those stairs, plus, it's right by an exterior door (which is probably R5 if the weatherstripping is perfect). The extra PEX at the bottom of the stairs is just noticable enough if you're in stocking feet and going upstairs. But even with that, there is a gentle flow of cooler air that enters the living room. An extra bit of PEX there and under each of the larger windows probably would have been a good idea for those stretches where we have several days below freezing.
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