heat exchanger to heat radiant floor

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Old 09-15-10, 05:20 AM
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heat exchanger to heat radiant floor

I have a 4 zone system with BB hot water.Plus I am using domestic hot water tank to heat radiant floor.I want to take out the hot water tank and replace it with a heat exchanger(HE) from the hot water boiler.Can't mix the two water systems(didn't know better 9 years ago when I put in radiant heat and pex doesn't have oxygen barrier). I need the exit(radiant floor heat side) of the heat exchanger to be about 130,the boiler runs about 180-190.Will use in grundfos 3 speed pump (15-58)on intake of HE off boiler.Radiant side of boiler has its own pump. Is there something (some kind of thermostat) that I can put on the exit side of the HE to say will turn off pump (boiler side)when the temp reaches the 130 that I want.
 
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Old 09-15-10, 03:03 PM
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Let me clarify a few things before we get started...

Is the existing boiler currently what you are using to heat the other 4 zones?

And the hot water heater is what is running the radiant floor?

And your goal is to add the radiant as a fifth zone off the existing boiler, isolated with a heat exchanger...

I'm pretty sure that's what you said, just wanna be sure before we all go off on a tangent.

How are the 4 existing zones zoned? With a circulator for each zone? or one circulator, and electric zone valves?

If one circ and zone valves, then you won't need another pump on the boiler side of the HX, just another zone valve. The boiler side of the HX will look like just another heating zone.

On the radiant side of the HX, you will need an expansion tank that is rated for radiant floor without O2 barrier PEX (plastic lined), air removal device, and water fill, pressure reducing, pressure relief, (and of course, the pump), etc... the normal stuff that a heating system would have, but it will seem redundant because it's a separate closed system.

There are a number of ways to regulate the temp in the radiant loop. You can run a fixed temp mixing valve, or, it can be 'controlled', i.e. warmer weather, cooler water.
 
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Old 09-15-10, 04:51 PM
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Originally Posted by NJ Trooper View Post
...

There are a number of ways to regulate the temp in the radiant loop. You can run a fixed temp mixing valve, or, it can be 'controlled', i.e. warmer weather, cooler water.
Or just get the heat exchanger sized right for the load and delta T between the boiler water temp and desired infloor water temp (and 130 F sounds pretty warm BTW).

This way it will respond to the boiler and outdoor conditions better.
 
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Old 09-16-10, 05:02 AM
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YES TO---Is the existing boiler currently what you are using to heat the other 4 zones?

And the hot water heater is what is running the radiant floor?

And your goal is to add the radiant as a fifth zone off the existing boiler, isolated with a heat exchanger...

YES HAVE WHOLE SETUP AND RUNNING FOR YEARS TO---On the radiant side of the HX, you will need an expansion tank that is rated for radiant floor without O2 barrier PEX (plastic lined), air removal device, and water fill, pressure reducing, pressure relief, (and of course, the pump), etc... the normal stuff that a heating system would have, but it will seem redundant because it's a separate closed system.


The four zones right now have separate pumps for each zone.Will be adding new pump for the fifth zone

I usually run boiler at about 180 most of the time.The return to boiler is only about 160 -165.If I used a mixing valve would it get the temp down to 140-145 max going in to HE.Was told the loss through the HE is only about 10-15%.This is the part I don't understand about mixing valve.How can you get lower than 160 if thats the water you are mixing with the 180 that the boiler is putting out.
This is why I was looking for a say clip on thermostat for the radiant heat side of the HE.
 
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Old 09-16-10, 03:11 PM
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Originally Posted by bill1925 View Post
YES TO---Is the existing boiler currently what you are using to heat the other 4 zones?

And the hot water heater is what is running the radiant floor?

And your goal is to add the radiant as a fifth zone off the existing boiler, isolated with a heat exchanger...

YES HAVE WHOLE SETUP AND RUNNING FOR YEARS TO---On the radiant side of the HX, you will need an expansion tank that is rated for radiant floor without O2 barrier PEX (plastic lined), air removal device, and water fill, pressure reducing, pressure relief, (and of course, the pump), etc... the normal stuff that a heating system would have, but it will seem redundant because it's a separate closed system.


The four zones right now have separate pumps for each zone.Will be adding new pump for the fifth zone

I usually run boiler at about 180 most of the time.The return to boiler is only about 160 -165.If I used a mixing valve would it get the temp down to 140-145 max going in to HE.Was told the loss through the HE is only about 10-15%.This is the part I don't understand about mixing valve.How can you get lower than 160 if thats the water you are mixing with the 180 that the boiler is putting out.
This is why I was looking for a say clip on thermostat for the radiant heat side of the HE.
Run the HE at boiler water temp, and temper the new system water with a mix valve off the HE and before the pump.
 
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Old 10-16-10, 06:45 AM
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Originally Posted by TOHeating View Post
Or just get the heat exchanger sized right for the load and delta T between the boiler water temp and desired in-floor water temp (and 130 F sounds pretty warm BTW).

This way it will respond to the boiler and outdoor conditions better.
Typically selected 50-70 plate models of brazed heat exchangers for radiant floor heating. However, it may vary according to your needs, outdoor temperature, heat loss through the house, etc.

5x12 inch. (1-1/4 inch MNPT) Stainless Steel Copper Brazed Plate Heat Exchangers
 
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