I have a 4-ton Hydro-Temp combination heat pump. The manufacturer gave, what I thought was, a vague diagram for the plumbing of the electric water heater(unpowered) on the water to water side for my radiant floor(basement slab).

To re-heat the water(Load) they said to draw from bottom drain and return to cold inlet on top. My plumber used 1" copper and the supplied B&G 1/6th HP pump. Radiant supply from hot outlet on top, return to a tee in cold inlet pipe, radiant piping was done in 3/4" copper.
 
The problem I found was, when both the floor and tank were calling, the radiant return would dead head at the tee, no water circulating in the floor, even thought the taco 007 was running. Plumber tried a venturi tee, didn't work. I then had the plumber seperate the pipes that were at a tee. Radiant return went to the cold inlet on top, Load return went in to Temp & pressure port in the side of the tank, already had a low pressure valve in the piping.

I have run the system like that since Jan 2011. The tank temp has been set at 95*F. Delta T starts out at about 30*F when the floor first calls. 2 zones, basement w/1200' of 1/2" pex-al-pex, garage w/600'. Main problem has been temps of water going out to the floor are only 95*F until the tank calls for re-heat, then temps drop quickly because of cold return water in the bottom of the tank being picked up by Load piping at the drain, then returned to T & P port near the top of the tank. That water basically goes across the top of the tank and right out the hot supply to the floor.

1. Would tee have worked if both systems were plumbed in 1" pipe? And if radiant return was straight through the tee w/load coming in on the angle of the tee?

2. I have thought about switching the in and out of the Load, so it draws from T & P port and return to the drain tee at the bottom. I think that may short cycle the reheating, don't want that. Moving the sensor up to the middle of the tank might help?

Sorry for the long winded post, just trying to be detailed.

Thanks for reading, ChrisJ RI 

got a sketch?

I will try a sketch

Another question.
The tanks ports are all 3/4". Does using 1" pipe make for more flow? I would think not, a 3/4" hole can only flow so much water.
ChrisJ

Posted By ChrisJ on 05 Mar 2012 09:08 AM
Another question.
The tanks ports are all 3/4". Does using 1" pipe make for more flow? I would think not, a 3/4" hole can only flow so much water.
ChrisJ

The limitation on flow of a short section of 3/4" in a  1" line is negligible compared to the difference in pumping head presented by 100' of 1" compared to 100' feet of 3/4".  That said, you only need as much flow as you need, and most radiant systems don't need or use 1".  But if yours IS  plumbed mostly with 1" the  hit in volume you see by a few feet of 3/4" dip tube in a tank or something  is really "the statistical noise"- the number of ells & tees in the 1" could have as much an impact on flow as a short section of 3/4".

Thanks for the reply Dana,

The first way it was piped didn't seem right, sending both radiant return and load return into cold inlet.

The way it is plumbed now is just messing up the tank stratification, wasting some of the 95* water.

The system has worked OK this year but it has been mild here in New England.

ChrisJ

I've plumbed hot water heater tanks in various ways and found that it works best to plumb heat to radiant floor off the hot fitting on top and return to the bottom drain hole using a tee. The water to be heated by the heatpump or other heat souce draws off cold fitting with a tee and returns also to the bottom drain tee. Plumbed this way statification yields the hottest water for the radiant system and the sediments remain in the tank.

55 gallons is a small buffer tank size. How many tons of the 4 ton heatpump used for water heating?

What is the target flow rate you are trying to push through the 3/4" piping? There will be some headloss but it might not be significant. The headloss calculatons depend on the flow rate. The greater the flow rate is the greater the headlosses will be. High headloss resulting in lower than designed flowrate will increase the delta T.

The heat pump is a dual compressor system, 1 1/2 ton for stage 1, 2 1/2 ton for stage 2 and both run for stage 3. The radiant is set up to run on the 2 1/2 ton compressor, so stage 2 max.

I don't know what the target flow rate is, I am sort of reverse designing the system trying to figure out where things went wrong (or not so right). I know I should get more flow to drop the delta T, but how much more pump?

Do you alter the dip tube? My tank says it has some special "rotoswirl" dip tube.

Having both returns tee into cold inlet originally didn't work, one flow stopped the other. 1" pipe for heat pump return went straight through tee, 3/4" pipe for radiant return into the 90* of the tee.
 
ChrisJ

55 gallons should be enough for 2 1/2 tons. I'm trying to imagine your piping. Is the system closed loop? How many circulators are you using and which models? Where are the circulators located in the system?

Yes it's a closed system.

Radiant side: 3/4" copper pipe, supply draws out of hot at top of tank, 2 zones, 2 Taco 007's. Basement zone is 30' X 40', 4- 300' loops 1/2" pex-al-pex. garage zone: 40' of 5/8" pex-al-pex feeds 2- 300' loops. Return pipe goes into cold at top of tank.

Heat pump side: 1" copper pipe, supply draws from tee in drain at bottom of tank, B&G 1/6 HP pump pushes water to heat pump, return goes into Temp & pressure port in the side of the tank near the top.

ChrisJ

I looked at your schematic. It looks ok, although I don't like drawing out of the bottom of the tank because sediments collect there. It should work the way its plumbed, except...where's the expansion tank? Are you pumping away from the expansion tank ?

Yes there is an expansion tank, water is being pushed through it, it's on the 1" return pipe from the heat pump to the tank.

ChrisJ 

"The way it is plumbed now is just messing up the tank stratification, wasting some of the 95* water." It looks like you're plumbed well with good selections for equipment (circulators, buffer, loops). Sorry I can't recommend any changes besides what I mentioned about not drawing off the bottom of the heater tank.

What temperature do you have your garage set at? If you are pumping 10 gal/min to the floor ( I don't know if you are or not) then in 5 minutes with a return water temp of 65 degrees then the whole tank will be close to 66 67 or 68 degrees without the heatpump running. I guess what I am trying to say is if everything is working right, You are going to pull the buffer tank temp way down with just 2 1/2 tons reheating the water.

I had the garage at 58*-60*F most of the winter, very mild this season in RI. Water returning from garage zone 65*F.

When the tank is at 95* and the garage calls for heat, it takes about 10-12 min of water circulating before the heat pump starts re-heating, basement zone takes about half that, 6-7 min. Temp probe is slipped in between the insulation and tank about 1/4 the way up from the bottom of the tank. Heat pump is set to re-heat at 84*F.

The supply temp to the floor drops to about 78-80* and the heat pump can maintain it, even gains temp if its just the garage calling, but runs for hours sometimes.

I am going to look into a circulator that can produce more flow in the floor, get the delta T down.

ChrisJ

Most of the geothermal manuals says to size 1 gallon for each 1,000 btu of heating in first stage...in this case, 55 gallons is bigger than recommended!

Thanks Surviverguy, Roger, Aces

Before next winter I want to build a solar collector and water storage tank. In the storage tank will be a coil of pex as a heat exchanger. I want to send the radiant return water through that exchange before it goes back to my 55 gal tank.

Adding another 200-300' of pipe to my already low flowing floor will require a bigger circulator. I just don't want an energy hog pump killing my overall efficiency. There must be an ECM pump that would work in this situation.

ChrisJ

You could add two closely spaced tees on the return side from the floor to the tank and add a small (30 watt?) circulator to the solar loop. You would use a differential controller to turn this small circulator on when there's heat available and either one of the zone pumps is operating. Inject the solar heated water into that cool return water. Look at primary/secondary pumping. The solar loop would use piping at least one size smaller than the return piping.