circuit loop length

Mark Eatherton

Numerous times. It spreads the heat out, and keeps the head reasonable.

Also used it on a snowmelt system. Nothing easier than running long 400' loops straight from one manifold at the top of the hill to another manifold at the bottom.

Interesting to hear the mod cons deal with the reverse function as the hot water comes out of the slab, headed for the other end of the system.

Graingers sells a real neat programmable timer for the reverse function. We build our own reversing valves using ESBE bronze valves and motor.

ME

Wild Rover

circuit loop length

I am finishing a radiant heat job and just discovered that my guys installed the tubing for one zone at different lengths. It was designed for 3 circuits @ 200' each (3/8 tubing) but i now have 3 circuits of 170', 200' and 230'. Will this make it too difficult to balance the circuits?

Brad White

Who among us does not like a challenge?

The ideal as you know is to get all circuits within 10% of each other, if not equal. 200 feet is about as far as I would go, so call that the median. Your 230 foot loop is of course 15% over, the 170 footer 15% under.

At 0.30 GPM per circuit,(1.65 feet per 100 feet of length pressure drop), your 200 foot median circuit would have a pressure drop of about 3.3 feet of head.

The 170 foot circuit would have a pressure drop of about 2.7 feet of head.

Your 230 foot circuit would have a pressure drop of about 3.6 feet of head. (IF all have the same flow- not a given necessarily.)

Each of these is within reason in range of being dealt with using a balancing valve. The longer circuit would be fully open as it defines the circulator head (contributes the higher portion, not indicative of the total head by itself). The shorter runs would be throttled accordingly.

There is no information to say that the 230 foot circuit is the most or least critical. Of less concern to me than the pressure drop and flow rate is the temperature gradient across the circuit. If this is more of an interior loop, maybe finishing up in an interior space, I would not worry about it.

If it is the primary exterior circuit, it may require that you use a slightly higher supply water temperature on a design day, which has a ripple effect on the shorter circuits taking the same higher temperature.

My $0.02

Brad

Wild Rover

Thanks

Thank you for your input. It sounds like i can enjoy whats left of the weekend and address this issue in a good frame of mind on Monday.

Rocky_3

Better than my situation

Got a call from a concrete plant. They were adding 22oo sq. ft. of new office space. Already had the tubing installed, concrete poured, walls framed, Buderus boiler sitting on a stand. Just needed me to come out and give an estimate on hooking up their tubing and boiler piping. I got there and saw three 1/2" pex loops sticking up out of the slab in one corner. I asked the manager where the other manifolds were? He said, "We just have the one manifold". I said, "But you only have three loops to service 2200 sq. ft." He said, "Yesssssss....", starting to get concerned over my concern. I asked him how close the centers were, thinking maybe they were at 2 foot centers or some other scenario. He said, "As per the salesman at the wholesaler, we put them 9" on center." I said, "Let me take a look at the ends sticking out real quick". Results? One loop was 742', one was 545', one was 402 feet. Longest loop, assuming no glycol and water temp of 120 degrees would require approximately 34 feet of head to even push one gallon of flow. I told him what the issure was. He just hung his head and said, " I let the concrete finishers put the tubing in. They said they knew how." I said, "I bet you got a good price, huh?"

Rest easy, you really have no problems at all at 220 feet!

Gotta go now, I have to go hook up a jet engine to a pump to push some flow for these guys.

Regards,
Rocky

Joe Billow_6

I can not find the post but didn't someone, I think Hot Rod, post something about using two mixing valves to alternate the supply to both ends of the circuit. It may not work but may be worth a try. I know of a shop that has one circuit about 600-700' I was going it on when I got some time.

Rocky_3

Joe,

Yep, there is a 4-way actuator that reverses flow just for such conditions. Siggy actually wrote about it in a past issue of PM magazine, and I believe, as you wrote that Hot Rod also either installed such a system or wrote about one. These guys are still trying to go cheap. I put in a Taco 13 just to service this loop: 1 gpm flow at 34 feet of head. Told them this was so borderline that there is NO way I will guarantee performance. I really think they are going to have to spend some money to fix this properly, but as yet, they are unconvinced.
Regards,
Rocky

Rocky_3

Mark

Can you give me a little more detail on how you do it? What equipment, controls etc? I would really appreciate it.
Thanks
Rocky

Joe Billow_6

Mark,

I too would really appreciate more info on this.

Thanks, Joe