I'll state for the record that I'm a newbie. I'm a DIY homeowner. I purchased a radiant system from a company that targets the DIY audience and I installed the system exactly as they instructed me to. The good news is that it works!.....Mostly. But now I'm trying to configure it so it's running as efficiently as possible. So I'm hoping this forum can give me some advice.
About my setup....
We live in a cold climate (northeastern US). The house is newly built and only 950 square feet total. It has one bedroom, a large main room, and a mudroom (ceilings in main room and bedroom are vaulted). These act as 3 separate zones. The mudroom and bedroom are small enough that I was able to install one continuous pex loop for each of those zones. The main room has four separate loops in it that branch off from a manifold. The layout is so small that I was able to home-run these loops (ie. the source and return manifolds are located right next to the boiler itself).
I have a closed system. The heating unit is only for radiant heating (not used for domestic water at all).
I'm using an American GT-240 (http://www.americanwaterheater.com/residential/tankless/gt-240-nih
What do I need help with?.....
It's only been in operation for a couple of months. Last night was a cold night. We noticed that the system was not able to maintain the thermostat's set temperature in the rooms (they were 5 degrees colder than set).
Our boiler heat output temp setting was 125 F. We raised this to 130 F and I know we can raise it up to a max of 140 F if needed. I've honestly wondered which is more efficient......do I keep the output temp low and run the pumps for a longer period of time? Or do I raise the output temp and run the pumps for less time? Since this is an on-demand system, there is no tank holding water (unless you count the water in the tube-runs as a "tank").
On a semi-related note.....while each zone has its own pump, our setup has a "helper" pump that comes on whenever any zone is called. This pump is near the inlet side of the boiler. There is also a by-pass loop built into this system with a ball valve on it. Originally, I had closed this valve to force all of the hot water to go through the zones. Then I started researching my issue this morning and started reading up on thermal shock. This is when I looked at the system and saw that my inlet temp was down to 82 degrees while my output temp was 125. I've read that the delta T should never be less than about 20 degrees. So I opened up the bypass valve and the input temp jumped up to over 100.
I was told originally that the purpose of this bypass loop was to prevent the helper pump from pulling water through zones that were not calling for heat. (So if zone 1 was turned on but not zone 2 and 3, the by-pass loop would prevent the helper pump from pulling water through zones 2 and 3.) But now, I'm thinking that this is there to prevent thermal shock to the system. Any thoughts on this? Should this bypass valve be fully opened, fully closed, or partially opened?