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Piwoslaw · 01-19-11, 12:42 PM

AC_Hacker asked me to post what I know about how hydronic floor heating allows a heat pump system to be more efficient, compared to normal wall radiators.

A heat pump system gets more efficient when the water temperature is lower, which can be had by increasing the area of heat exchangers (radiators). This means either increasing their size, or their number, or going with a totally different approach and using the whole floor area for heating. This brings the water temperature down from a max of 85°C to a max of 55°C. Normal temperatures in a floor heating system are usually closer to 40°C. This is also good for increasing the efficiency of a system with a condensing furnace, since it only condenses (efficiency above 100%) when the temperature of the returning water is below the dew point.

A side effect of using hydronic floor heating is that heat is distributated much better than with wall mounted radiators, allowing the room temperature to be 1-2°C lower, which leads to further savings.

As for how to plan and build such a system, the only "real" info I found was: when laying the water tubes, there should be at least 8 meters of tubes in each square meter of floor area, you may want slightly more in "cold" areas, ie close to doors and windows. I could not find anything about what type of tubing to use or what diameter (I assume there is only one standard diameter?). Of course, the tubes should be in loops, plumbed in parallel, not series, to distribute the heat more evenly and to reduce pumping losses. There should be a reflective layer underneath, and foam insulation under that. Tiles are good for covering it, wood is not.

Another thing that increases the efficiency of almost any heating system with radiant floors is a heat buffer. The buffer allows the heat pump (or whatever other heat source) to work at its most efficient speed/setting, while heat is taken from the buffer only when it is needed. Low temperature (floor) heating allows the buffer to give up more heat before needing to be charged again. Great for when you have a cheap source of heat (solar, electric with night tariff, etc.). It also allows zoning of the heated part of the house, which allows you to save by reducing heat use in unoccupied rooms.

01-19-11, 12:42 PM	#40
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	AC_Hacker asked me to post what I know about how hydronic floor heating allows a heat pump system to be more efficient, compared to normal wall radiators. A heat pump system gets more efficient when the water temperature is lower, which can be had by increasing the area of heat exchangers (radiators). This means either increasing their size, or their number, or going with a totally different approach and using the whole floor area for heating. This brings the water temperature down from a max of 85°C to a max of 55°C. Normal temperatures in a floor heating system are usually closer to 40°C. This is also good for increasing the efficiency of a system with a condensing furnace, since it only condenses (efficiency above 100%) when the temperature of the returning water is below the dew point. A side effect of using hydronic floor heating is that heat is distributated much better than with wall mounted radiators, allowing the room temperature to be 1-2°C lower, which leads to further savings. As for how to plan and build such a system, the only "real" info I found was: when laying the water tubes, there should be at least 8 meters of tubes in each square meter of floor area, you may want slightly more in "cold" areas, ie close to doors and windows. I could not find anything about what type of tubing to use or what diameter (I assume there is only one standard diameter?). Of course, the tubes should be in loops, plumbed in parallel, not series, to distribute the heat more evenly and to reduce pumping losses. There should be a reflective layer underneath, and foam insulation under that. Tiles are good for covering it, wood is not. Another thing that increases the efficiency of almost any heating system with radiant floors is a heat buffer. The buffer allows the heat pump (or whatever other heat source) to work at its most efficient speed/setting, while heat is taken from the buffer only when it is needed. Low temperature (floor) heating allows the buffer to give up more heat before needing to be charged again. Great for when you have a cheap source of heat (solar, electric with night tariff, etc.). It also allows zoning of the heated part of the house, which allows you to save by reducing heat use in unoccupied rooms. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.