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Old 03-09-13, 02:21 PM   #21
Drake
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I definitely want radiant floor heat even at an added expense(if any) because I already have designed for a high mass concrete floor for passive solar storage and really like the evenness of radiant heat. MikeS, if I understand you prefer a holding tank approach to feed floor. I have found a dual xfer loop tank w/ elec back up that, though a little money, would let me off peak heat w/elec and let me add at least two other backup heat sources(wood, solar, DIY geotherm) if wanted/needed with just one tank. Does that seem reasonable? "Over heating" of our core winter living space in not an issue as over 1/3 of total space is 3 season and excess heat is easily distributed to that space and then usable in those times. Making a solar designed space that is zero net 70-80% of the time(at least for heat) is doable without great complexity. So my design for retirement home is a winter core space that can be lived in and heated for comfort for those cold periods. Also work for the few days/nights summer cooling is needed in my area. But it is true that the advances in energy conserving building techniques/design haven't followed thru to the concern for cost/energy saving heat/cooling plants to match them in the US. Being "green" shouldn't always have to cost more.

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Old 03-09-13, 02:41 PM   #22
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Don't get me wrong. I don't have much against radiant heat as a heat source. I'm not seeing your point about humidity or dust though.

Humidity control during a heating climate in a well sealed house is not needed but the most important part is that there is no difference between forced air and radiant heat in that respect. You don't remove or add moisture to the air in the enclosure with either method unless you install a humidifier or rehumidifier to the forced air system.

Dust control can't happen period without air movement, you need to pass the air through a filter to remove the dust. So I'm not sure where you were going with that either. Granted I'm not saying it's a big issue or anything, just trying to figure out where you were going there because a decent filter on a forced air system is going to clean the dust out of the air that passes through it. With the radiant system the dust will stay suspended in the air and precipitate out on surfaces and get kicked up by human activity. Either way you go it's probably better to avoid carpet versus making a decision over whether or not your heating system moves air.

With a low energy building you can centralize your heating and cooling and the entire structure will remain the same temperature. I've noticed that the further that temperatures deviate towards the outdoor temperature are the least insulated even to the point where I can block both return and supply vents from my most insulated room and have it warmer in that room than my least insulated room that has air flow. So you are right about not needing the hydronic floor plumbing everywhere if you are aiming for close to passive, or at least something around the R's of 5,10,20,40,60 with reduced glazing in the home design, although slab on grad you remove the R20 component and if going with R3ish energy star windows you'd need to reduce glazing to under 15% window to wall, IMHO. The only trouble you get into with that idea though is reduced ability to recover from large setbacks without either temperature differentials or long setback durations. I might be the only person with a 25 degree setback(for both away, sleeping, and often for entire 10 hour 4 day workweeks) though, oddly one that I'd probably want to keep even with a low energy building.

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Old 03-09-13, 05:52 PM   #23
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Don't get me wrong. I don't have much against radiant heat as a heat source. I'm not seeing your point about humidity or dust though.

Humidity control during a heating climate in a well sealed house is not needed but the most important part is that there is no difference between forced air and radiant heat in that respect. You don't remove or add moisture to the air in the enclosure with either method unless you install a humidifier or rehumidifier to the forced air system.

Dust control can't happen period without air movement, you need to pass the air through a filter to remove the dust. So I'm not sure where you were going with that either. Granted I'm not saying it's a big issue or anything, just trying to figure out where you were going there because a decent filter on a forced air system is going to clean the dust out of the air that passes through it. With the radiant system the dust will stay suspended in the air and precipitate out on surfaces and get kicked up by human activity. Either way you go it's probably better to avoid carpet versus making a decision over whether or not your heating system moves air.

With a low energy building you can centralize your heating and cooling and the entire structure will remain the same temperature. I've noticed that the further that temperatures deviate towards the outdoor temperature are the least insulated even to the point where I can block both return and supply vents from my most insulated room and have it warmer in that room than my least insulated room that has air flow. So you are right about not needing the hydronic floor plumbing everywhere if you are aiming for close to passive, or at least something around the R's of 5,10,20,40,60 with reduced glazing in the home design, although slab on grad you remove the R20 component and if going with R3ish energy star windows you'd need to reduce glazing to under 15% window to wall, IMHO. The only trouble you get into with that idea though is reduced ability to recover from large setbacks without either temperature differentials or long setback durations. I might be the only person with a 25 degree setback(for both away, sleeping, and often for entire 10 hour 4 day workweeks) though, oddly one that I'd probably want to keep even with a low energy building.
Forced air does entrain the dust in the air far more than rads or floors do. It doesn't prevent dust from being produced but it does float around more which is why air cleaners are sold so much. You also notice the on/off periods which you don't with floor heating or cast iron/steel rads. Sound is also a lot more noticeable from a ducted system. Also, I can run a Grundfos alpha pump with 10w which is not possible with forced air.

The humidification issue is more to do with gas or oil burners that dry the air too much, which brings in the need for humidifiers of some sort. Of course this is less of an issue if an air handler is used off a low temp water supply. From a comfort point of view you need a higher minimum water temp to run an air handler than you do to heat a floor at the same outside conditions. I think the tighter the house the more we have to worry about excess humidity than adding it.

I would love to setback my house as much as you do but my spouse sometimes works from home and she is always cold so while I love the radiant heat, I won't get that level of control that warm air heat gives. I can live with that problem.

Drake wondered about my need to use a tank. If the control has a PID that looks at outdoor temp and/or humidity as well as indoor temps, the lowest water temps can be used to provide the heat and it can be designed to note when the passive is heating up the space at a fast rate. I use the floor tubing to distribute heat from over heated areas to less heated areas. I am all for multiple inputs to the tank but we have a hard time controlling the result with the tanks we have here. I wish we could get some of the European tanks but they don't meet our stupid pressure requirements.
But that is another topic.
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Old 03-09-13, 08:21 PM   #24
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My first suggestion wd be to turn down the boiler temp to 130 deg max for both safety and savings; I try to keep ours lower than that. Our radiant floor, which has been in operation for 26 years, is fed water at 110 deg. The water comes out of the heat exchanger at 120-125 and is modulated down to 110 by means of a tempering valve which injects some of the return water into the incoming hotter water. The house stays at a never changing 71 degrees. The circulating pump turns on and off a bit, but in general it runs for several hours at a time as the floor changes temperature very slowly, so the thermostatic cycling of the pump is kept to a minimum. I believe you will save more energy with lower water temperatures than you could ever save by trying to shorten the pump on time.
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Old 03-09-13, 11:40 PM   #25
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MS, I am interested in your use of hydro tubing flow to redistribute heat throughout floor do you do this with just continuous flow or additional tubing and pumping. As the depth of my space only has the south half exposed to direct passive solar this would definitely help control hot spots. A mixing valve only adds heated water to a loop if the temp in the floor loop requires it correct? I don't know if it is possible but if solar could ever heat the floor mass and thus floor loop water beyond a comfort temp is there a way to remove/shunt/temper w/cooler water the loop? Maybe just controlling(shades/blinds) the windows would be the simplest overheating solution. My wife is the same if I give her 80 degree heat in the winter she will always want it 80. She wants it 75 in the winter and 65 in the summer.
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Old 03-10-13, 07:53 AM   #26
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My method is to keep the looping as simple as possible, which means one zone per level and the tank is good because it is a big mixing chamber but most of this is about control and measuring the temps in the right places.

Michaels system, above, is very traditional and If his insulation levels are reasonable he could be turning down the mix temp and boiler temp by +20F, especially given his location. This is why I like outdoor control on boilers AND mixing valves. There are times when a floor heat system only needs 75F water. Of course, during most of those times, the passive can supply redistributed to the colder parts of the house. Solar hot water can help to charge the tank as well.
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Old 03-10-13, 12:35 PM   #27
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Quote:
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MS, I am interested in your use of hydro tubing flow to redistribute heat throughout floor do you do this with just continuous flow or additional tubing and pumping. A mixing valve only adds heated water to a loop if the temp in the floor loop requires it correct? I don't know if it is possible but if solar could ever heat the floor mass and thus floor loop water beyond a comfort temp is there a way to remove/shunt/temper w/cooler water the loop? Maybe just controlling(shades/blinds) the windows would be the simplest overheating solution.
Hello Drake: Sorry, but I don't understand the first sentence above. I'll just give a short description of our system. It is extremely simple, no zones or zone valves. Ours is a 2000 SF house with 1100 SF having floor heat. No heat in the bedrooms. The heated floor has ten 220 LF x 1/2" OD tubes run in large coils at 6" spacing except somewhat closer in the baths. Two manifolds serve the ten loops. One circulating pump delivers hot water from a heat exchanger to the floor, and a second circulates hot water from our Bock water heater to the heat exchanger. When the thermostat calls for heat, both pumps, which are 1/25 hp, run. The heated water could come directly from the Bock heater eliminating one circulator, but I believe the literature that says you shouldn't keep introducing new, oxygenated water into the floor system which could degrade the tubes, so a heat exchanger isolates the floor water.

A tempering valve adds *cool* water to a system. In DHW systems, it acts as a safety device to prevent scalding. They can be preset to provide a specific, lower output water temperature regardless of the input temperature. In a floor system, the valve injects a measured amount of the cooler water coming back from the floor into the hotter water going out to the floor in order to lower its temp to the acceptable level. In our case, it reduces the heated water from 120-125 to 110 deg.

My experience with radiant floors tells me that one must abandon all concepts of quick or instant heating or cooling. We have a very small thermal mass, i.e. 3/4" tile over 1-1/2" concrete. The heat tubes are in the concrete. This is all on plywood with insulation under. Still, if we turn the system off, and the house cools down, it takes a full day to bring the house back up to 70 degrees. Larger masses would be far slower to change, but the advantage for me is the stability of the heat once it is at the optimum level. I'm trying to speak to your questions, so sorry if I'm getting off the subject, but what I mean is that if you have overheating in a room because of solar gain, taking heat out of the mass of the floor will be a long, slow process. My guess is that, yes, you should simply shut the blinds.

I suspect that water heated in solar collectors can be used for floor heat, but the problem is always one of heat storage. A 120 gallon water tank heated by solar to 140 degrees and distributed to your floor until the temperature of the water is down to 100 will provide you with only 38 kBtu, and there are additional shortcomings. The 120 gallon tank, if heated by some alternative source, will be full of hot water in the morning when the solar collectors start to perform unless you take measures to prevent it, so there won't be any place to store the solar gain. Timing and storage are two of the big issues with solar and radiant heating. The sun is out when you don't need additional heat; it's cold and dark when you do.

I've got to stop. I think all my blah, blah is likely to be trying your patience. I've thought about this stuff a lot and installed quite a bit of it over the years, and I can yak about it forever. Sorry. mm
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Old 03-11-13, 07:29 PM   #28
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Thank you for all the info, you are not boring me. To try and clarify my beginning question(and I think you answered it) you use the floor loops that you heat with to ALSO redistribute heat around floor. I favor the KISS method when ever I can and it is easy for me to understand heating low temp water for a high mass floor and circulate it much of the time for an even space temp. This method though can not easily take advantage of any high temp water heat storage(off-peak elec, solar, wood heated etc.) without getting complicated(and lag time from high mass also adds complexity). In a very low heat demand living space the simpler on demand method may be a better choice and put money into PV panels on the roof and store elec in the grid. I will have a large optimal pitch south facing roof just for that and we will be grid tied. We are also at the head of a windy valley so some small scale wind generation is also being planned. I am familiar with the operation of indoor therm controls but these outdoor ones being spoken of are they primarily for radiant floors? If I googled them could I find info on how the work? I'm not trying to build a zero net home, just a very conserving one.
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Old 03-12-13, 02:56 AM   #29
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I'm not certain what is meant by outdoor controls unless it is the case of a temperature sensor on the sunny side of the house that anticipates a warming trend and shuts down the circulators in advance of when the indoor thermostat would do the same to prevent overheating the home. Best of luck with your radiant heating and solar projects. I'm new to this board, so I'm plowing my way through all the history, and I'm somewhat daunted by it, but I feel lucky to have stumbled upon it. mm

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Old 04-14-13, 05:57 PM   #30
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FWIW, I'm running my radiant floors at a constant supply temp of ~115F which makes the floors feel quite comfortable. The controller only turns on and off the pump.

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