Adding radiant under floor heating to bathroom from existing loop

ryank

I have an existing closed loop, single-zone, baseboard system in our house. I'm renovating a bathroom and was thinking of rather than putting a radiator back in, and adding electric tile heating mats, I would convert just that room to hydronic radiant floor. The thought being that the radiant floor would serve double-duty both heating the space and warming the tile floor. The trick is I want it to use the same existing closed loop (boiler, and single circ pump) and zone thermostat so that the bathroom heats in parallel with the rest of the house.



My initial thought was as follows. Use one or two diverter/venturi tees to divert a small volume of water to a new radiant loop, and mixing valve to both bring the temperature down and allow me to calibrate the temperature of the bathroom to match that of the rest of the house. I would prefer not to have a secondary circ pump as I still want the primary loop to control whether this new secondary loop is on or off, no second zone/thermostat as the room is only 60 sf.



I understand I've got some calculations to do to determine if the size venturi tees will provide enough flow through the radiant loop, but in theory, can create a simple secondary loop this way? Thank you!

icesailor

Radiant Loop:

That might work for you. I've never seen it work for anyone else.

I can see no reason why it would work as drawn but it might work for you.

ryank

whoops.

hmmm, I just realized this there will be no way to circulate the radiant loop when the mixing valve closes on the hot supply...

icesailor

Loopy:

That's right.

ryank

solution?

So is a solution to forget the venturi tees (use standard tees) and simply add a small circ pump that is also activated by the primary loop's thermostat? Could I literally use a Taco Priority Zoning pump with integrated switching relay and just split the signal from the existing thermostat (one to primary loop pump, one to new pump)?

STEVEusaPA

You're gong to need another circ

Running in series with the main loop. Right after the 3 way, pumping into the radiant. Keep in mind it may affect the rest of the main loop. And drop the Venturi tees if you add the circ.

SWEI

small circ

Check out the B&G Ecocirc e3-4 (also sold as the Laing Ecocirc E1) for a small zone like that.  Miniscule power consumption and onboard speed adjustment lets you dial in your delta-T quickly.

Mark Eatherton

Nice try...

I've had that exact same idea, and I came to the same conclusion you did. Once the 3 way closes its hot port, your circuit gets nada in the way of flow. A no go.



Now, you could use the two tees as shown, and put in UltraFin instead. Either that or bare naked tubing. The only problem I could see then would be the possibility of the bathroom overheating, and if that became an issue, you could then install a non electric TRV with a cap tube to limit the bathrooms temperature.



But then, if the bathroom got too cool, the TRV can't make a call to the physical plant for flow and heat, but its better than what I presume you've got now...



I have a friend who took a somewhat similar approach, except that they didn't use a mixer to limit the temperature to the RFH zone, but instead used 3 venturi tees. One for supply, one for return, and one to blend cooler return water with the RFH supply water for a lower supply to the RFH zones. They had to add remote cap tube TRV's later but it did work. Their heat sources were all set up with an ODR that started at 140 and ended at 180.



ME

KCA_2

Hmmmmmmm

Seems like you have a couple of issues here...

1.  Not to overheat the floor (Above 85degF +-)

2.  Not to overheat the bathroom



and it would be nice to keep it simple...  right?



I ran into a valve by Danfoss.... An ESBE VTC thermic valve....  It's used to regulate the supply or return water to or from a boiler...  It comes with different temperature elements (122 degF, 131, 140, 149, 158, 176) and the valve only fully opens when the water temp reaches +- 18degF above the element that you install...



If you use the return water temperature that would be about 160degF....  Using a 158degF element that means that the valve would open about 20%....  allowing only a trickle of water through the tubing keeping the heat down...  or a 149degF element would fully open at 167degF....  That would be about 80% open? 

I don't know your bathroom and what the load is...  if any...  so you may not need much higher temp water ....



No additional circulators, electric components...  Keep it simple...



http://na.heating.danfoss.com/PCMPDF/ESBE%20VTC%20Datasheet.pdf



You likely would still need a venturi tee...



Oh...  It's under $200



I hope this helped



 :-)  KCA

Mark Eatherton

Not sure this will work Ken...

Your assumption of a 20 degree DT goes against what I typically see in the field. Typically less than a 10 degree DT,even at design condition.



I fear that the 3 way would lock up and flow would cease, same as we projected with an adjustable 3 way valve.



To the original poster, maybe you should consider the use of UltraFin heat emitters (high temperature), and use the venturi tees as previously described, along with a non electric thermostatic control valve. It wouldn't allow the bathroom only to call for heat, but whenever the heat was on, the bathroom would be getting controlled comfort.



There is more than one way to skin a cat.



ME

furnacefigher15

Why not this way?

Put a dedicated pump in for the infloor, and install a mixing valve. Place the pump on the AB (mixed port)



Regardless of valve position, the pump sees 100% flow. Run the pump of a high voltage t-stat in the bathroom, or use a low voltage one and a relay.



The bath will heat anytime the baseboard is hot.



Scrap the venturi's. Use standard tees. Also add valves on either side of the in floor loop for purging and service.

ryank

finished

Thank you for all the feedback to my question. This is what I ultimately did, a taco mixing valve and a taco circ pump with integrated relay. The pump can take a call for heat directly from the house's sole thermostat. I'll be able to drop the radiant loop's water temperature down incrementally with the mixing valve so that the temperature of the bathroom is consistant with the rest of the house.