Adding radiant floor to existing baseboard hydronic heating system

241comp

I have a new-ish home (circa 2001) which has a 4-zone hydronic baseboard heat system utilizing a Burnham Revolution boiler. The circulator (Taco 007) is on the supply side and the zones are controlled by zone valves on the return side.

We are adding a sunroom (~250sf) which is being constructed on top of an existing concrete patio slab (with full footers). The existing slab is lower than the final floor, so we have some space to work with. The proposal we have received is to add a radiant floor by insulating on top of the existing slab and then pouring an additional 3" slab on top of the insulation with a hydronic loop in it. The proposal suggests we use a 3-way mixing valve (Honeywell AM-1 R) to get 120-deg water from our existing boiler.

The radiant floor as engineered has a 119-deg required temp and 0.74GPM flow rate. The proposal does not include a separate circulator for the low-temperature loop, however, a circulator is shown in all of the "typical installation" diagrams provided by Honeywell for the installation of this mixing valve. Is the use of this kind of mixing valve to add a low-temperature loop to my existing system reasonable without an additional circulator?

241comp

I couldn't attach this to the original post, but I did my best to draw a rough layman's diagram of the the system.

bburd

The new radiant floor will need another circulator on the floor loop side because of the mixing valve. There is no other way to get low temperature return water from the floor to mix with the high temperature supply to produce the low supply temperature needed for the floor. The baseboard zone return will be too hot.

241comp

Ok, that makes sense and is what I am concerned about.  Is there a way I can convince my HVAC guy of this fact?  Maybe documentation about this from a manufacturer?

Would you recommend this circulator be on the return side of the low temp loop, or the supply side?  Will it be fighting with the main circulator to generate flow if both circulators come on when only this zone is calling for heat, since the only return path for the main circulator is a very restricted flow out the mixed-outlet or flowing out the cold-inlet.

My current system has what I would call "dumb" wiring.  No zone controller, just a couple transformers and a bunch of direct wiring to the control valves with a single demand circuit that turns on the boiler and circulator. Is the proper way to do this to use a zone controller that offers independent circulator control?

gyrfalcon

Good morning, 

My home has a comparable system- old school cast boiler, 2 zones of baseboard heat and a south facing sunroom/ solarium which is connected to my living room and entryway.  This sunroom, approximately 10x30 ft, has always been either too hot or too cold.  I thought about adding radiant floor heat or a loop of baseboard fin tube to help heat the room in the winter. After some thought about layout, controls, and summer time solar gain. We decided to install a 12K Mitsubishi mini split.  This has satisfied the heating and cooling needs for that room plus some. . In fact due to my house’s unique build , my sunroom, entryway, living room/ dining room  , 1 bedroom and part of kitchen are all supplemented and maintain a 68-72 degrees all year.
 
Just a thought for you to consider if it’s feasible .

 I love my boiler but for what it’s worth the mini split was an excellent investment for us. 
 

pecmsg

241comp said:

Ok, that makes sense and is what I am concerned about.  Is there a way I can convince my HVAC guy of this fact?  Maybe documentation about this from a manufacturer?

Would you recommend this circulator be on the return side of the low temp loop, or the supply side?  Will it be fighting with the main circulator to generate flow if both circulators come on when only this zone is calling for heat, since the only return path for the main circulator is a very restricted flow out the mixed-outlet or flowing out the cold-inlet.

My current system has what I would call "dumb" wiring.  No zone controller, just a couple transformers and a bunch of direct wiring to the control valves with a single demand circuit that turns on the boiler and circulator. Is the proper way to do this to use a zone controller that offers independent circulator control?

If you need to "Convince Him" find another contractor!

241comp

That's a very fair recommendation and if it were solely up to me, I would definitely switch HVAC contractors at this point. Unfortunately, this is a subcontractor (Hydronic HVAC) of a subcontractor (overall HVAC) in a fairly extensive remodel being run by a General Contractor. This plus some other circumstances mean that I have relatively little control over sub selection at this point. I may be able to convince my GC that they need to make the HVAC sub find a different Hydronic sub, if I can show that the Hydronic guy is not properly designing the system. But I'll have to convince 2 layers of self-confident contractors that their guy doesn't know what he is doing.

JMWHVAC

Subcontractor of a subcontrator. Sorry, but thats scary.

hot_rod

No need for the zone valve on the radiant, you do need a circulator in the H, mixed port.
Thermostat turns on the circulator

241comp

hot_rod said:

No need for the zone valve on the radiant, you do need a circulator in the H, mixed port.
Thermostat turns on the circulator

That's an interesting approach. Without the zone valve, will the main circulator end up circulating hot water through the radiant loop when another zone calls for heat and the main circulator turns on?

hot_rod

these are good piping options
https://www.pmmag.com/articles/84495-a-little-floor-warming-please-john-siegenthaler

241comp

Thanks for all the help. This far.

The approach you suggested above with just a circulator would be "wild hot water bypass" from figure 2 and requires a loop circulator and flow restrictor?  Any reason the same wild hot water bypass wouldn't work with a return side zone valve (though it seems unnecessary), other than the need to wire it to open the zone valve when the circulator comes on?  The advantage I would see to the zone valve is that the bypass loop isn't constantly flowing 180-deg water when another zone causes the main circulator to turn on.

hot_rod

Yes, either the bypass with some balancing, or a zone valve for 100% shutoff

241comp

Thanks for all the info. Armed with this knowledge, I have had another conversation with the contractor and they have agreed to follow one of the reference diagrams that Honeywell provides with the particular mixing valve we are using. This will include use of a circulator on the radiant loop and a zone valve on the return.

241comp

I've drawn another diagram as I understand the install will be completed. And now I have another question: If the main circulator runs when there is a call for heat only from the radiant loop, the only return path for water pushed by the main circulator would be to counter-flow the cold input on the mixing valve (effectively turning it into an output). This is because all of the other returns have zone valves on them. Is this a problem? If so, there are 2 solutions I can think of:

1. Add a bypass with flow restrictor so that the main circulator always has an available return.
2. Control the main circulator to only run when at least 1 of the 4 remaining zone valves is open (call for heat on one of the other loops).

Are these appropriate approaches, and would it be necessary to implement?

hot_rod

Not ideal. The main boiler circ is pumping into the hot port and the radiant is also pumping the mix valve. The flow resistance in the floor loops is higher than
across the valve, so flow will cross in the valve.

However the radiant circ is also in series, sort of, with the boiler circ, so I’m not sure how they will get along. That is why either the closely spaced tees, or a balance valve to force the correct gpm around the loops

If any other loop opened with the radiant, that changes the hydraulics also

I’d like to see how a delta p type circulator would work with that piping?

Wiring will be a bit more complicated, a zone valve and two pumps need to run at once. With a radiant call.
But on zone valve calls, only one circ.
The Caleffi ZCV relays can do that as they have 3 relay/ pump configurations.

241comp

Do I understand correctly that you are suggesting something more like this?

hot_rod

An automatic balance valve there might be ideal. Get a 2 or3 gpm valve and the valve and delta P circ would settle in to exactly that, conserving a small amount of pump electricity
The pump should rev up as zones open, as you have a combination parallel and primary/ secondary boiler loop.

https://fergusonprod.a.bigcontent.io/v1/static/4003482_4623441_specification