HW recirculation with tempering valve grundfos comfort

[BMWpowere36m3]

I want to retrofit my existing HW installation with recirculation, due to addition and longer runs. I saw an older thread which suggested adding an aquastat switch, to keep the recirculation line from reaching full hot water tank temp if using a tempering valve.

So my existing installation is [inside basement]: water meter > PRV > expansion tank > cold line tees [indirect tank inlet & tempering valve]. I don't have any check valves (unless they're in the tempering valve) and the only expansion tank is right after the PRV near the water service entrance/meter.

I've looked at these Grundfos Comfort (10-15) pumps, which have 3 models... a timer based, timer + temperature, and a "adaptive" + temperature. I recall seeing an older Grundfos document, but I can't find now that suggested not using the adaptive model with a tempering valve, unless the valve is disabled. In the application notes is states:

COMFORT circulator pumps are suitable for the following:

• single-loop systems
• branched systems (balancing valves are recommended)
• open-vented systems
• pressurised closed systems with or without mixing (tempering, anti-scalding) valves
• all types of tank water heaters.

I was considering using the timer + temperature model (TDT), but I also don't see any specific installation requirements in their documentation (online). The built-in aquastat is variable, but not by the user... it monitors for max temp in the return line every 12 hrs and sets the cut-off/in temperature is 7-13 degrees F lower.

What should I consider when I install this pump OR open to other suggestions? I found this diagram online, a few questions:

• should I relocate the existing expansion tank (green block)?
• do I need those two check valves in the diagram?

*edit* the US comfort models have an integrated isolating valve and Non-return valve.

 

[Fitter30]

Need to know brand, model and pipe size of mixing valve. From mixing valve to where your tying in, pipe size and type of pipe. Piping from tie in pipe type, size and length. This info is for design head to size pump.

 

[Sponsor]

 

[BMWpowere36m3]

Need to know brand, model and pipe size of mixing valve. From mixing valve to where your tying in, pipe size and type of pipe. Piping from tie in pipe type, size and length. This info is for design head to size pump.

The mixing valve is a Honeywell AM-1 3/4" sweat union. Around the indirect tank, the piping is 3/4" copper, which transitions to 3/4" PEX for trunk and later 1/2" branches.

With this recirc loop, it would be a 3/4" PEX loop ~ 140 ft + 8 ft of 3/4" copper which would make up the outlet from the mixing valve and return from the pump to cold feed.

 

[Fitter30]

Grundfos 10-15 should give you 3 gpm. Using 180' of pipe 32' extra for fittings 3/4" 90°= 2' and 3 gpm through mixing valve, 4 gallons of water 150' 3/4" m

 

[BMWpowere36m3]

Grundfos 10-15 should give you 3 gpm. Using 180' of pipe 32' extra for fittings 3/4" 90°= 2' and 3 gpm through mixing valve, 4 gallons of water 150' 3/4" m

I wasn't really concerned about flow rate... for the recirculation loop I assume it'll be low when there's no demand. When a fixture is open, the furthest distance would be about ~ 75 ft and the pump wouldn't be helping. As in, the force driving the water would be the regulated pressure off the cold side, no?

I was concerned about backflow, proper check valves and expansion tank positioning.

 

[Reach4]

I was concerned about backflow, proper check valves and expansion tank positioning.

Expansion tank usually goes on the cold supply line. You should not have to add a check valve, I don't think.

 

[BMWpowere36m3]

Expansion tank usually goes on the cold supply line. You should not have to add a check valve, I don't think.

I already have the an expansion tank, right at the PRV... the question is if you add those other check valves per the diagram, maybe the expansion tank point needs to be different perhaps?

I also found this diagram with the Honeywell tempering valve. Though a quick look, made my head hurt... my indirect tank only has a single cold supply (bottom of tank) and hot out (top of the tank).

The diagram separates the recirculation return into the tank, from the cold water supply into the tank... There's a nuance I'm missing, but since both "colds" are connected inside the tank... I'm not sure.

 

[Reach4]

I am confident you are fine. There is no check valve between the water heater tank cold inlet, and your thermal expansion tank. Turn off the WH, or go to vacation mode,before you close the service valve.

In addition to running hot hot to the dishwasher thru a separate pipe than what supplies the hot to your sink, you can also run it to your washing machine I think.

 

[BMWpowere36m3]

I am confident you are fine. There is no check valve between the water heater tank cold inlet, and your thermal expansion tank. Turn off the WH, or go to vacation mode,before you close the service valve.

In addition to running hot hot to the dishwasher thru a separate pipe than what supplies the hot to your sink, you can also run it to your washing machine I think.

I do have valves already at the WH to isolate it or whatever, but I only close the main service entrance valve if I'm away for an extended period of time. That service entrance valve is before the water meter. So the plastic line comes through the foundation>ball valve>water meter>PRV> expansion tank> then all the "supply" runs through the house.

Here's a look at what's currently in place, no recirc setup yet. I guess I'm not sure which diagram to follow. Is it as simple as plumbing into a "loop" from the hot outlet of the WH, with the recirc pump on the return side and "tee" it into the cold inlet of the mixing valve?

 

[Fitter30]

Expansion tank by main is all you need don't. Don't need one by the water heater.