Adding a Thermostatic Mixing Valve

EricPeterson

This is the year I hope to redo my near-boiler piping to add better boiler protection from condensation and thermal shock. To date I've been using a system bypass with a ball valve diverting heated water back to the return. My boiler is a Burnham ES heating a converted gravity system with three zones and CI radiators over four floors.

I plan to use a thermostatic mixing valve, in particular the ESBE VTC511 thermic valve with either a 131 or 140 thermostat (Burnham says: "The ES2 has been designed to accept return water temperatures as low as 110°F without complicated piping or additional controls"). A piping diagram is shown below.

Pertaining to this diagram, I have a few questions:

1. Is there any recommended spacing for the piping, and the spacing of the circulators?
   
2. Are there recommended circulators to use in this application? (I am planning on using the NRF-22, which is in service today and works great.)
   
3. Is there any way this will not work, i.e. will hot water somehow fail to circulate effectively through the system?
   

I settled on this as it seems to me to be the simplest and most effective solution.
Any comments on this plan, or these components, are welcome.

Thanks,
Eric Peterson

hot_rod

Nothing against Danfoss products. Take a look at the Caleffi 280 also. In a system like you describe a single pump should be adequate to flow the conversion piping, the valve and the boiler.

https://www.caleffi.com/sites/default/files/file/01223-23_na.pdf

EricPeterson

@hot_rod - a single circulator would be great if it worked for my system.

However the diagrams for the 280 do not provide a clear indication that this would be the case:

• the diagrams all show the pump on the return side. I do not know if this matters.
  
• Operating Principle diagrams show a buffer tank, does this also represent a system?
  
• The Application diagrams pertinent to my setup show a second circulator, in addition to components that I lack (mixing valve). It does not seem apples-to-apples.
  

As for the valve itself, if I understand it correctly, the temperature sensing is on the supply side. If for example I use a 140F thermostat, mixing would start when the supply temperature is 140F. Once open it would start mixing with the return water. If the return water were say 65F then with a 50/50 mix the return water would drop to (140+65)/2 or102.5, which would then lower the supply water temperature to 102.5 plus whatever gain occurs as the water passing through the boiler is heated.
The valve would then close until the supply water reached 140F then the cycle would begin again.

I don't know the heat rise, which depends on the boiler and the flow rate.
Suppose though that the heat rise was 37.5 degrees, in this case that would be a problem in that the valve would then remain open with low return temperatures, until the water in the system warmed up sufficiently.

I doubt that the heat rise would be that much. Or maybe a higher temp thermostat would be needed.
Does Caleffi have a recommendation for the proper thermostat to use in a converted gravity system?

Does the above explanation make sense?

Thanks,
Eric

hot_rod

All the thermostatic mix valves work on the same principle, temperature sensing across the heat motor inside. The main difference between protection thermostatic is the high Cv and fixed temperature. Inside, the same sensor/ heat motor. 

The way you pipe them determines if they are mixing or diverting. The sensor inside is  responding to return temperature in a diverting or protection application

The Caleffi drawings are just showing a tank as the load as they are mostly/ always used on wood and bio boilers connected to buffer tanks.

The tank could be substituted with any high mass distribution, radiant slabs,  large gravity types. Its just an example drawing to show the concept.

They all need to work around a hystersis. So a 130 valve with an 18 degree would need to see 148 before the bypass port closes 100%

I assume the second pump on the Esbe is to assure adequate distribution flow, maybe for small tube radiant for example not for the valve to regulate accurately?
Using the valve for conventional boilers tied to low temperature distribution 

EricPeterson

@hot_rod - thanks again for the information.

I sent an email to Caleffi sales requesting technical support and got a callback within an hour from someone named Matt. He was able to answer all my questions. I appreciate this great service!

The Caleffi looks to me to be a nicer product than the Danfoss so I will go with the 280.
I like the union fittings and also the 4 "Temp gauge pocket wells" where you can attach a temperature gauge (I think the Danfoss has these as well).

According to Matt @ Caleffi:

• Yes you can install this valve using a single circulator.
  
• The temperature sensing (thermostat) is located where the supply and return water mix, so the 140F thermostat should provide more than adequate protection for the system. Since Burnham says 110F is OK the 115F thermostat might work as well.
  

One thing I forgot to ask was the expected service life of the thermostat element.
If anyone has any information on that it would most appreciated.
Also if anyone is using the Caleffi or Danfoss thermostatic mixing valve I would like to know how those are working.

Using this valve, along with the IAS, ATF-12, and a single circulator, should help to meet my design goals of a simple system that works well.

Eric

hot_rod

I had this 280 on my wood boiler for a number of years, it worked perfectly.

The biggest concern with thermostatic valves, any brand, is water quality. Dirty, or hard water can scale up the innards and the regulation accuracy can go off, or the cartridge can fail if the valve scales up completely.

After all your renovation work I would run a cleaner for a few days, at high temperature if possible. Dump that water, add low hardness, low TDS water and maybe a squirt of hydronic conditioner. These squirt cans make it easy to inject the cleaners.

Have you checked the water quality coming into your home? A hardness test kit is a good inexpensive start, find them on Amazon. TDS would be another good number to know. Maybe take a sample to a wholesaler that has test kits or send it in to Rhomar, Fernox or any that offer water testing.

Download this Idronics for the simple answers to hydronic water quality.

This will be good for all the components, boiler, valves, pumps, heat emitters, etc.

I would go with the 130 cartridge. I'd be nervous about running 115 or lower return for extended periods.

EricPeterson

@hot_rod - the water is my system has been there since I split the main house into two zones and added some TRVs, which was in 2000 so 23 years ago. Since then the same water has been circulating. When I've drained water from the compression tank it looks pretty clean, just a little discolored.

Any work I do will be isolated to the near-boiler piping as I have shutoff valves for the rest of the system.
I've never known of a need to flush the system.

I'll take a look at the Idronics article though.

Eric