In the remodel that we are currently doing we are going to put in a new boiler and use a bunch or turn of the century radiators. The new boiler runs at about 160-180 most of the time. One patticular (back porch) will have in slab pex tube for heat. In most installations I’ve seen them use tempering valves for in floor heat . My question is do we really have to use a tempering valve in in floor concrete? does it have somthing to do with pex tube, or is it just that way for folks whom install wood flooring above (which we don’t plan on doing). Lost in the 120 temp valve
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Don't think I would want to stand on a concrete floor that was near 120 degrees very long.
Don't know much about radiant heat floors, but logic says the tempering valves are to maintain a constant moderate slab temperature and flow rates. A high temperature might cause excessive cycling.
Dave
ever walk on hot asphalt in yer bare feet?
Ahh, I can see a light bulb over yer head now.
Max floor temp for non wood floor coverings , i.e. tile is about 90deg.
Theoretically, it is possible to reduce flow through your radiant zone so the floor doesnt "see" all that 180 deg. water, but I wouldnt do it. Mixing valves are like 80 bucks after all.
If you have made some insulation and air infiltration upgrades, you should be able to heat your house way less than at 180. I have turn o' the century cast iron rads too, and can heat my old house for much of the heating season at less than 140. Alot of times my mixing valve sees water and doesnt even mix it-which is what you are trying to do.
Hopefully you went w a condensing boiler, otherwise you will have to set up your boiler to avoid such low return water temps which will damage it.
Check out outdoor reset too, will vary water temps according to outside temps, big money saver.
The purpose of the tempering valve is really to maximize the efficiency of the boiler/radiant panel combo. Generally speaking, the most efficient way to run a radiant panel is at the lowest supply temperature that will cover the heat loss on a design day (average coldest temperature day, which is, for example, -10* in SE MN), and then modulate the supply temperature for warmer days.
So you should have some idea of how many BTUs you will need to supply to that slab to maintain comfort for the occupants, and then take into account tube size, loop length (usually 250 ft max for 1/2" PEX) spacing, insulation under and at the perimeter of the slab, and control strategy. If you figure that the slab will keep the ambient temperature in the porch at 70* with X* supply temp, then you may need to temper the water or not.
You can also "rule of thumb" all this by figuring 15 btu/sq ft output with 120* water, if the porch and slab are well insulated with normal glass area...maybe 20 - 30 btu/sq ft if there's lots of glass and/or no insulation under and around the slab.
And then you could always supply the porch with its own zone valve or circ pump, and then embed a slab sensor that controls flow to the porch via a relay, and go ahead and pump whatever the boiler puts out into the slab to maintain, say, a 70* - 80* slab temp, and then play with the control to get it to even out. Potential gotcha there is that if the supply temperature is too high, the slab will over heat so quickly that the flywheel effect will cause discomfort on the porch until the load carries some of those excess BTUs away.
There is alot of margin for error in a radiant panel...and if you pay attention to some of the basics and overkill a bit on your control strategy, you'll end up OK...the only goal being to avoid not being able to get the ambiant temp over 65*, or under 75*.
Here ya go...there is standards for floor tempertaures...bottom line provides temperature, right hand side tells us what percentage of people will be unhappy as the floor temperature changes.
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RBean
http://www.healthyheating.com
http://www.healthyheating.com/blog
Edited 1/9/2005 10:53 pm ET by RB
not onluy would it be uncomfortable for you, but the extremes of temperature would shortent the service life of the concrete. 110-114° is about right for it
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I agree the lower the temp the better. Here's a bit more info:
As of this month, my current PCA and ACI books specify the maximum allowable fluid temperatures in pipes embedded in concrete is 150 deg F.
Having said that, properly cured concrete will withstand much higher temperatures..thus reason why it makes a great fire separation material.
The actual fluid in pipes for heating is determined by a combination of the heatloss, floor covering R-value and tube spacing.
So a professional radiant designer or a Thermal Environmental Comfort Technician manipulates spacing and fluid temperature to reduce the number of fluid temperatures required for the project to keep control cost down with the objective of keeping the fluid temperature as low as possible for highest efficiency.
If the owner is willing to change the floor coverings to a lower R value then this results in lower fluid temperatures and less pipe. Improving the building effciency creates the same results.
Occasionally we'll hear things like you can't run 140 deg F or 160 deg F water in any radiant systems but the reality is those temperatures have little impact on the structural or material integrity of building materials and in fact where the heat load is very high and the R value above the floor we need the higher temps. The caveat is the output from a radiant floor is a nominal 2 Btu/hr/sf * deg F difference between the floor temp and the room temp. So a room designed for 70 deg F and limited to 85 deg F floor temp has a capacity of 30 Btu/hr/sf.
(85 deg F - 70 deg F) * 2 Btu/hr/sf *deg F = 30 Btu/hr/sf.
This tells us that any load greater than 30 Btu/hr/sf is going to need supplemental heat regardless of fluid temperature or tube spacing.
[Incidentally most floor coverings make great radiators. The only difference between carpet, tile or plain concrete is the required fluid temperature, but all floor coverings operating at the same temperature have the same output.]
Anyways, in concrete the largest concern has to with curing which is why you'll often see 90 deg F as the maximum allowed until the 28 day mark. In sub floor system sometimes we'll hear things like plywood delaminating or linoleum yellowing or other issues but in fact the temperature of plywood under a black shingle roof is far more abusive than radiant is...even when it comes to hardwood floors there is a lot of misinformation about radiant...fortunately most of the floor covering associations have dispelled these myths.
Is this useful information to all?
RBean
http://www.healthyheating.com
http://www.healthyheating.com/blog
Edited 1/10/2005 12:26 am ET by RB
Edited 1/10/2005 12:27 am ET by RB