I’m hoping that someone can help with my Hydronic Central Heat system. If you want to skip all the data and get right to the questions, just scroll down and look for this: ###
You can always refer back to the data if needed.
I just installed a new boiler after the old one went into nuclear meltdown. (don't ask ;-))
I installed this whole system when I built this home in 2003. I'm not a plumber or builder, just a DIY kind if guy. It's likely that I made mistakes on the original design and I'm just trying to get the system working the most efficiently that it can.
Here’s some info on the system, each item listed in order as it appears in the system.
1. Boiler: Trinity TFT 110,000 btu.
2. The primary loop is 1" copper.
3. Fill water tap. 12 psi
4. Air scrubber and expansion tank installed prior to main Circ pump.
5. Main Circ Pump is Taco 0011 (currently incorrectly installed, pump horizontal with motor vertical) This is a new pump that replaced the same kind.
6. Indirect 40 gallon hot water tank for DHW is tapped off main loop. Another Taco 0011 feeds tank. (seems like overkill, or am I missing something?)
7. In-floor hydronic Centra Heat system Tapped off Main Loop. About 5’ of 1” copper forms heat trap.
8. Central Heat return T’s in adjacent to CH feed. 1” Copper Heat trap installed on return.
9. Taco 0010 circulator installed vertically on outgoing heat trap.
10. Mixing valve installed, but currently closed.
11. ¾” pex delivers hot water to and from the zone manifolds on both levels of the house.
12. Zone valve installed just prior to Manifold.
13. Zone manifolds are Heat Link,
14. Loop tubing is ½” pex installed before concrete poured.
15. There are two zones on the main level, each with 5 loops per manifold.
16. I don’t know the exact length of the longest loop, but I estimate between 150-200’ based upon the area and the way it was done
17. Pex spacing in the floor is either 9 or 10”.
18. The floors are concrete poured on Insulated Concrete Forms, like this: http://www.quadlock.com/images/insulated_concrete_forms/floors/Quad-Lock_Quad-Deck_Corner_Illustration.jpg
19. No floor coverings are installed on the concrete floors. They do have a few area rugs on them.
20. The exterior walls of the house are also ICF's.
21. House is approx. 2500 sq ft on each of two levels (5000 total). The lower level is a walk out basement with the same ICF floors and walls as the main level. Up to this time, the lower level has never had hot water run through the floor. I am currently only heating the upper level, the lower level never gets much below 50 degrees even in winter and without heat.
22. I ran a heat loss calc recently based on this method:
I used a design day of 0 Degrees and inside temp of 68 F.
I came up with a total heat loss of 77,318 BTUH for both levels of the house, 50,679 for the main level. However, since the home is made with ICF's we have much lower infiltration than a normal 2X constructed house. So I applied a reduction to the infiltration calcs of 20%. This yielded a total heat loss of 68,718 BTUH and 44,000 for the main level. I did not apply loss to the main floor, though it may have been prudent to apply some.
23. The method above showed that approximately 7-8 gpm was needed to service the radiant heat system.
24. 12 feet of head based upon a 200 foot circuit length
Here's the issue; on the main level of the home the water temp going to the manifolds is 140 deg**; there is a 37 degree drop on the return manifold, and this is after the floor is up to temp and the thermostat is ready to shut off the heat call. This is also with only one zone calling for heat and only two of the 5 loops open on the zone getting heat. When both zones are calling for heat with all 10 loops open, I still get the same 37 deg drop. There is a 3/4” pex run from the main boiler loop to the manifold, of about 25’. I calculated that based on the Delta T of 37, that I’m getting about 2 gallons per minute of flow through the ½” pex. I have read that this is about ideal for ½” pex, but I believe that it could pass more water if the circ pump was up to it.
It’s now obvious that larger tubing would have better served for the loops, but it’s too late to change that as they are totally embedded in concrete.
Taco shows a Head Range of 9 for the 0010 pump. If these calculations are correct, it would suggest that the 0010 is not the right circ pump for the job. So here are the questions:
1. Is 37 degrees too much Delta T for this system?
2. If so, what would be appropriate? 20?
3. Is my flow calc of 2 gpm correct?
4. Do you think that my head calc (12) is correct?
5. Will a pump with more head range provide more flow through the zones with ½” pex, even if it is not the ideal flow rate for ½” pex? It seems that even a little more flow would bring down the Delta T and allow the floor to heat up more quickly. THAT my friends, is the goal of this novella.
a. Despite the high Delta T, the system does indeed heat the home very well, I’m just trying to speed it up and have it run at highest efficiency.
** I realize that 140 might be too hot, It can be lowered either at the boiler or with the installed mixing valve. What temp would be ideal and should I lower it at the boiler rather than at the mixing valve?
I’m sorry for the long post here, but I wanted to provide as much data as possible, since it seems that most people don’t provide enough when asking for help.
Thank you for your assistance!
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