return water temp

frank_48

what i have is a 44x76 building divided one room 30x44 with 3 loops one room 46x44 4 loops they are one 450 to 500' vanguard said i could go 500' with 3/4" if i set the thermo at 70 the room heat good but when the system comes back on if i wait 5 min and shoot the tubes i still get 25d difference no the perimeter is not insulated

frank_48

radient heat

im being told that a 15 degree difference in send and return temp is ideal the best i can get is 25 degrees what can i do to close the gap i have two inch foam down then 5 inch of concrete 3/4 b-pex on 12" spacing ive had 2 different places figure for pump sizing and they tell me i have a big enough pump think it need to travel through the loop quicker and my loops are not over lenth

Brad White_9

Heat Soak?

Frank,

How long has the system been running? 25 sounds like a cold slab condition at start-up, only better. Is the slab perimeter insulated also? Bigger losses there than you realize.

Just what are the tubing circuit lengths? How many and how equal are they?

And the ultimate question, Delta-T aside, how is the slab and how is the space performing?

jp_2

outside temps?

whats your outside temps right now? what do you expect for mid winter temps?
what type of wall and ceiling insulation?

how long has the 'heat' been on?

Brad White_135

Frank a couple of things....

The 500 feet of 3/4" pex is a little concerning, not insurmountable but pushing things. Most PEX runs like to be 300 feet or less as a safe default, less on smaller diameters. Varies, but at least you have a somewhat throaty tube working for you. If you had 3/8" or 1/2" you would be, if not screwed, at least not kissed in the process.

What is the pump you are using and what is your expected flow rate per circuit?

Without an insulated perimeter and especially (if and) once the slab warms, your heat losses will give you a snow melt system by default.

And as JP asked, where is the building and how cold does it get there?

frank_48

I live in lower michigan i havent got to play with it yet this season i just got the system late last winter i will get the pump sizes and exactly what i have and post them ive got r-19 in the walls 6" batt and 12"r-38 in the ceiling plus the inside is finished with 7/16 osb on walls and ceiling again from what little bit ive got to use this it makes the space comfortable but is it being as efficient as it can be

Brad White_135

Frank

Yes, the information will help but to be realistic I would not take performance in this weather as saying it will be fine when Canada sends her best....

What does the designer say? Do you also have the design parameters and what they are expected to do? We have the 12" OC and the substrate being concrete. Seems well enough insulated -not some cheap box- but what was the calculated heat loss?

If your 44 x 74 slab could put out 30 BTUH per SF, that would be just over 100 MBH output. Let's see what the designer says.

frank_48

i have a peerless pinnacle 140btu boiler boiler pump expansion tank then to a split with grundfos 15-58fc 3 speed pumps. i had 15-42 single speed pumps then the heating place im dealing with sent the 3 speed pumps to close my return temp gap but from what i see looking at the pumps the high setting on the 3 speed is the same as the sinle speed pump so i gained nothing. i also have not put the no burst into the system yet and im being told that this will push 10% harder.im running anti-freeze because im not heating both rooms full time i also put in a bypass loop between boiler pump and circulater pumps. not sure what heat loss and perameters are i laid tubing accoring to computer drawing that was sent to me by desighner and was told that with heat loss and everything factered in that this system will maintain 70 degrees at 20 below i will leave a # if you would advise me on the land line thanks frank

ALH_4

temps

Why are you shooting for a 15 degree dT? A 15 degree dT is pretty tight in my opinion. Is the floor noticeably uneven temperature? Are the loops embedded within each other or are they serpentine?

What is the supply temp? The higher your supply temperature, the more quickly heat is lost. Therefore dT is continually changing if you have outdoor reset. If you have a thermostatic mixing valve, your supply temperature is set at the temperature the system needs at design conditions.

In real life, dT is not really something to get too hung up on as long as one side of a room is not noticeably colder than the other. When designing a system, we assume a value for flow calculations, but this really has nothing to do with the actual heat transfer capabilities of the tube and flooring.

If you would really like to tighten the dT then you need a bigger pump. Try a 26-99 3-speed Superbrute. The pump body dimensions are identical to the 15-42. That way you have some extra pump to play with. Whomever sold you the 15-58 was obviously mistaken as to its capacity versus the 15-42. As you said, they are nearly identical.

-Andrew