Cast iron Rads and TRV's

Iron rads and TRV's are a match made in heaven.
Given that the air temp the TRV is "looking at" is nearly at floor level, there is no issue with it being mounted right next to the rad, if that is what you were asking.
You can also get TRV's with remote sensors that use a hydraulic "cap tube" to connect the TRV to the actually room temp sensor.

I don't use TRV's in my system, just the thermostat. One suggestion...use a t circulator on small zones with cast iron radiators.(bumble bee or the like) especially if you plan to "set back " the zone. This is my 4th year with cast iron radiators.....I hope I never have to live without them in the future. Way better then "baseboard" ...witch is way better then "hot air"....witch is one step up from a camp fire...

There are some recommendations in this brochure for pipe size depending on effective radiated area and pumping system. See the back page
https://file.ac/aFiAOXPm13Y/slenderized-product-literature.pdf

iceguy4 said:

I don't use TRV's in my system, just the thermostat. One suggestion...use a t circulator on small zones with cast iron radiators.

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A P pump like the Alpha that salecker has is really a great compliment to the rads with TRV's. No need to change pumps as you can pretty much dial in whatever T you want with the Alpha by varying the flow as it has 7 functions to play with. 3 fixed speeds, 3 constant pressure settings and autoadapt. I spend 95% of the time in fixed speed one, pumping up to about 2.5 gpm with a T of 20 +/- a degree or two, that gives me up to 25,000 Btu/hr drawing about 6 to 8 watts. When get near design temp I bump it up to speed 2 and and that gets me the 38,000 Btu/hr I need then.

Low temp radiant emitters, constant circulation with TRV control and ODR=Hydronic Nirvana. Popular in Europe where they take their hydronics very seriously.

Noah

!/2" is definitely large enough for your application,The reason the fittings on CI radiators are so large is that they were originally designed for ether steam or Gravity hot water. since you will be using a circulator larger piping is not necessary or even desired in this case.

I'm very familiar with TRVs having seem them installed on radiators throughout Europe, but I cannot understand how they would be integrated into a hydronic system. I am planning a system using cast iron radiators that would be highly zoned (each room being one zone), but my thought would be that this would be done with an individual room thermostat and a separate pump for each zone.

How would TRVs on each radiator work? Would there have to be constant pump pressure in all of the lines? If so, what if there is pressure via pump but no TRVs calling for heat - would there be pump damage?

If anyone can give a good explanation or point me to a weblink, it would be much appreciated. I haven't been very successful in researching this on my own.

DBoon said:

If anyone can give a good explanation or point me to a weblink, it would be much appreciated. I haven't been very successful in researching this on my own.

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Each TRV is a thermostat for the emitter it controls. The other key element is the use of a modern constant pressure ECM pump like a Bell & Gossett ECOCIRC, Wilos Stratos, or a Grundfos Alpha that senses flow resistance and will supply more flow for more zones/low resistance, less flow for fewer zones/higher resistance, or no flow for no zones/highest resistance.

Check out this link, starting on page 78

http://www.nyserda.ny.gov/Publicati...h-efficiency-hydronics-wood-fired-boilers.pdf

Re-hash with some great counter-examples:

http://phcc.cms-plus.com/files/2011Foundation/PDFs/2012ConventionHandouts/Distribution Efficiency - Siegenthaler.pdf

DBoon said:

I'm very familiar with TRVs having seem them installed on radiators throughout Europe, but I cannot understand how they would be integrated into a hydronic system. I am planning a system using cast iron radiators that would be highly zoned (each room being one zone), but my thought would be that this would be done with an individual room thermostat and a separate pump for each zone.

How would TRVs on each radiator work? Would there have to be constant pump pressure in all of the lines? If so, what if there is pressure via pump but no TRVs calling for heat - would there be pump damage?

If anyone can give a good explanation or point me to a weblink, it would be much appreciated. I haven't been very successful in researching this on my own.

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I have two zones in my house, one zone for each floor. The second story has three bedrooms and two bathrooms. There is a Buderus panel radiator, the modern equivalent to a vintage CI radiator in each of the five rooms. Each panel radiator has a TRV. There is a 1/2 inch pex supply and return for each radiator. A single pump, a Grundfos Alpha, on constant pressure setting 1 supplies all the water these radiators need. More GPM when it is cold out and less GPM when it is warmer outside. The TRV acts as a thermostat for each room. It is great!

Before the days where pressure sensing and speed control were integrated into the pump a hydronic system like this would require a pressure relief. Not so with a constant pressure pump.

Alpha pumps are awesome.

The main supplier I used when I did my project had no clue what an Alpha was.

Weird or what?

Hi DBoon,

DBoon said:

If so, what if there is pressure via pump but no TRVs calling for heat - would there be pump damage?

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As EW mentioned, an ECM circ is key. They don't suffer from dead heading like a standard circ that requires a pressure activated bypass in this type of install.

DBoon said:

but my thought would be that this would be done with an individual room thermostat and a separate pump for each zone.

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I recall you have a relatively small heat load for the planned system from a previous thread of yours-something like 22,000 BTU/hr, maybe? A single ECM should easily handle your needs. Way better than multiple pumps, IMO.

Here is a pic of my heat distribution setup:

Each of the seven loops of infloor radiant has a capillary tube TRV. Of course this would work great with CI rads with standard TRVs as well.

For more reading on this subject check out The Wall http://www.heatinghelp.com/Forum . Search constant circulation with TRV's and you'll have plenty to read through. Lots of pros over there, including a few of the generous pros who post here as well.

Noah

ewdudley said:

Each TRV is a thermostat for the emitter it controls. The other key element is the use of a modern constant pressure ECM pump like a Bell & Gossett ECOCIRC, Wilos Stratos, or a Grundfos Alpha that senses flow resistance and will supply more flow for more zones/low resistance, less flow for fewer zones/higher resistance, or no flow for no zones/highest resistance.

Check out this link, starting on page 78

http://www.nyserda.ny.gov/Publicati...h-efficiency-hydronics-wood-fired-boilers.pdf

Re-hash with some great counter-examples:

http://phcc.cms-plus.com/files/2011Foundation/PDFs/2012ConventionHandouts/Distribution Efficiency - Siegenthaler.pdf


View attachment 128673

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Thanks for posting the links, very informative.

Surprised to see my no power dump zone is pictured on page 36 of the first link.

gg

maple1 said:

Alpha pumps are awesome.

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I agree and I must admit I was a little envious when I saw this http://eshop.fbcstore.co.uk/epages/BT4148.sf/en_GB/?ObjectPath=/Shops/BT4148/Products/"LK 810 Eco"/SubProducts/L181059

The LK Acaso 810 loading unit with 3 speed Alpha instead of the 15-58 that we have. Hopefully we will see more 60Hz ECM options on this side of the pond in the future.

Noah

ewdudley said:

Check out this link, starting on page 78
http://www.nyserda.ny.gov/Publicati...h-efficiency-hydronics-wood-fired-boilers.pdf
Re-hash with some great counter-examples:
http://phcc.cms-plus.com/files/2011Foundation/PDFs/2012ConventionHandouts/Distribution Efficiency - Siegenthaler.pdf

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Excellent links, EW. Required reading for all who frequent the Boiler Room, IMO.

Noah

Hello All,

Thanks for the additional links and explanation. This all makes perfect sense now. I've (overall) liked the TRV operation when I've used them, but I didn't know how they worked when connected to the boiler system. One thing I've found with TRVs is that they really are made for a set it and forget it mode - they are not great for a quick blast of heat in an area. Now I know why that would be.

Question - the TRV would go into the case iron radiator supply inlet, correct? If this is a few inches off the floor, how well would the TRV work to regulate room temperature, given that (floor) temperature could be a few degrees colder than mid-height?

I'm familiar with John Siegenthaler and someday I will just have to buy his book. I also found the heatinghelp.com site to be an indispensable resource when I was researching and determining what I should in replacing my oil boiler at my existing house. For some reason, I never thought to look there for info on TRVs.

For those who remember my various previous posts, I'm going to be re-habbing an old house over the next three or so years. The plan is a wood boiler with 500-800 gallons of unpressurized storage and a massively zoned cast iron radiator distribution system. My overall belief is the "KISS" principle and TRVs really fit the bill with one constant circulation pump and a simple zoning valve near the user/radiator.

Hi Thomas,

The Burnham radiators I've looked at have the inlet and outlet at the bottom. See https://file.ac/aFiAOXPm13Y/slenderized-product-literature.pdf. Do you know of other alternatives, aside from used units (which I wouldn't rule out either).

I've also bought radiators from Shafter Brothers in Quebec, but these are piped bottom inlet/outlet as well.

I think bottom in & out is OK too. When the hot enters, it goes up, then drops as it cools.

Hi maple1, salecker, I know bottom in/out works - my oil boiler and radiators are set up that way. I am wondering if having the TRV down near floor level affects the operation given that floor temperatures can be quite a bit cooler than temperatures 24" off the floor.

DBoon said:

I am wondering if having the TRV down near floor level affects the operation given that floor temperatures can be quite a bit cooler than temperatures 24" off the floor.

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I don't think the placement will affect operation in any way. You might have to set the dial a little higher with it closer to floor vs at waist height but once you find where to set the dial to achieve the temp you want than the TRV will simply open or close to meat that set point.

These things respond really well to solar gain, occupants, heat from cooking, etc. It's pretty cool watching the flow meters on my manifold to see what loops are flowing and how much.

Noah

^ We have some panel radiators that are different sized, the TRV height makes no difference. A few adjustments over the course of a week or so until the room is comfortable, then lock the dial in place and it stays comfortable.

Thanks for the feedback on TRV placement. Much appreciated.