Open vs closed floor loops?

Drake · 03-23-13, 09:27 AM

I don't believe I have seen much said about open vs closed systems from those who are hydronic floor heating. Though I have read the descriptions of there differences what are working floors using? Which is more favorable towards low heat/high mass designs with just one or two loops? Is the type of pex(O2/non-O2) a factor(I know it affects material,metal, choices)?

There are very convincing arguments by professional for each type from what I've gathered.

AC_Hacker · 03-23-13, 11:33 AM

Quote:

Originally Posted by Drake

I don't believe I have seen much said about open vs closed systems from those who are hydronic floor heating...There are very convincing arguments by professional for each type from what I've gathered.

Another consideration would be that all of your domestic hot water would have to flow through several hundred feet of hot PEX before you used it.

I still have serious questions about plastics being used in food and potable water production & distribution. There have been lab studies that the additions to plastic that insure flexibility, can mimic some human hormones, like estrogen in particular, and that even minute amounts can have a measurable effect.

The plastics manufacturing industries have come down like the hammers of hell on these studies.

-AC

Drake · 03-23-13, 03:24 PM

True, the real health risks in things thought as good practice, even just a couple decades ago, are now being recognized with time being used. Molds, VOC's, legionnaires etc. Sorting out what may be the best engineering solution from what may be unsafe is another in the many variables that work into deciding best way to go. Something is making all the fish turn female, giving us three eyed and legged frogs, scramble bees. But at near sixty not sure what can be done to extend my life when my pregnant mother smoke and drank, I chewed a lead painted crib all day, made silver pennies with mercury bare handed and spent 3/4 of my life in a radon filled basement shop.

Ryland · 03-23-13, 09:09 PM

How would you do an open loop? just have your potable water run in your floor and back in to your water heater? seems sketchy to me, but my water heater is designed to work as a boiler as well.
I would rather not drink water out of plastic, so altho I have PEX in my house, my drinking water is copper and iron pipe.
One reason I can see for having closed loop is that in all the closed loop systems I've installed we added stop leak and conditioner that is supposed to protect the boiler and metal fittings.

Drake · 03-23-13, 10:46 PM

I understand a closed loop separates domestic water from floor loop and eliminates oxygen but it needs xchng loop, air tanks etc. Only need one pump in a simple open system. Pex is used and is code certified for potable water supply. Just trying to understand choices to be made.

Ryland · 03-24-13, 09:02 AM

Even an open loop system is going to need an expansion tank, otherwise you are going to blow the pressure relief valve, You have this huge mass of cold water in your floor and as that heats up it expands, with domestic hot water the water isn't normally being heated all that much without at least a little hot water also being let out of the system, the amount of water in the system is also much smaller because you have 100's of feet less tubing.
If you have your own well with a pressure tank then you might be ok, that tank should absorb the expanded water, but if you are on city water each house is required to have dual check valves to keep rusty water in your pipes from back flowing in to the water mains.

Drake · 03-24-13, 11:10 AM

Good point, I do have an over sized pressure tank(just got a larger one than needed clearance priced over smaller one) and well. I was thinking that an open system could provide limited floor cooling, within the limits of dew points, if exterior water tap was in the line and outside water was drawn thru it in summer.

Mikesolar · 03-24-13, 11:34 AM

You have to be careful about expansion tanks. There are ones for hydronics heating (which will rust out in a open system) and different ones for domestic hot water. The air charge is different and the material construction is different.

Drake · 03-27-13, 03:47 PM

Does it then take a special tank to be a buffer tank for a closed system or will most any of the single or double coil tanks be OK? Would a double coil tank let you use top coil for Hydro closed loop output/return and lower for alternate heat source, solar, wood etc.??

Mikesolar · 03-27-13, 06:29 PM

The buffer tank can be open or closed (HX or not) depending on what you want it to do. If you have a heat pump or solar system the buffer tank has different reasons for being. With the solar, obviously it is a question of containing as much heat as possible, with the HP it is all about having minimum run times and keeping the changes in loop flow from affecting the flow through the HP.

A double coil tank is good if there is dead water ( solar) on the bottom coil and boiler on the upper coil. I wouldn't use a HP on the upper coil because the flow rates through the HP may not match the needs or performance of the coil. In this case it is better to use an open tank (or single coil) and put a HX on the output for DHW. We also want to avoid using more pumps than we need to so this has to be carefully done.

03-23-13, 09:27 AM	#1
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	Open vs closed floor loops? I don't believe I have seen much said about open vs closed systems from those who are hydronic floor heating. Though I have read the descriptions of there differences what are working floors using? Which is more favorable towards low heat/high mass designs with just one or two loops? Is the type of pex(O2/non-O2) a factor(I know it affects material,metal, choices)? There are very convincing arguments by professional for each type from what I've gathered.

03-23-13, 03:24 PM	#3
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	True, the real health risks in things thought as good practice, even just a couple decades ago, are now being recognized with time being used. Molds, VOC's, legionnaires etc. Sorting out what may be the best engineering solution from what may be unsafe is another in the many variables that work into deciding best way to go. Something is making all the fish turn female, giving us three eyed and legged frogs, scramble bees. But at near sixty not sure what can be done to extend my life when my pregnant mother smoke and drank, I chewed a lead painted crib all day, made silver pennies with mercury bare handed and spent 3/4 of my life in a radon filled basement shop.

03-23-13, 09:09 PM	#4
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	How would you do an open loop? just have your potable water run in your floor and back in to your water heater? seems sketchy to me, but my water heater is designed to work as a boiler as well. I would rather not drink water out of plastic, so altho I have PEX in my house, my drinking water is copper and iron pipe. One reason I can see for having closed loop is that in all the closed loop systems I've installed we added stop leak and conditioner that is supposed to protect the boiler and metal fittings.

03-23-13, 10:46 PM	#5
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	I understand a closed loop separates domestic water from floor loop and eliminates oxygen but it needs xchng loop, air tanks etc. Only need one pump in a simple open system. Pex is used and is code certified for potable water supply. Just trying to understand choices to be made.

03-24-13, 09:02 AM	#6
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	Even an open loop system is going to need an expansion tank, otherwise you are going to blow the pressure relief valve, You have this huge mass of cold water in your floor and as that heats up it expands, with domestic hot water the water isn't normally being heated all that much without at least a little hot water also being let out of the system, the amount of water in the system is also much smaller because you have 100's of feet less tubing. If you have your own well with a pressure tank then you might be ok, that tank should absorb the expanded water, but if you are on city water each house is required to have dual check valves to keep rusty water in your pipes from back flowing in to the water mains.

03-24-13, 11:10 AM	#7
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	Good point, I do have an over sized pressure tank(just got a larger one than needed clearance priced over smaller one) and well. I was thinking that an open system could provide limited floor cooling, within the limits of dew points, if exterior water tap was in the line and outside water was drawn thru it in summer.

03-24-13, 11:34 AM	#8
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	You have to be careful about expansion tanks. There are ones for hydronics heating (which will rust out in a open system) and different ones for domestic hot water. The air charge is different and the material construction is different.

03-27-13, 03:47 PM	#9
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	Does it then take a special tank to be a buffer tank for a closed system or will most any of the single or double coil tanks be OK? Would a double coil tank let you use top coil for Hydro closed loop output/return and lower for alternate heat source, solar, wood etc.??

03-27-13, 06:29 PM	#10
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	The buffer tank can be open or closed (HX or not) depending on what you want it to do. If you have a heat pump or solar system the buffer tank has different reasons for being. With the solar, obviously it is a question of containing as much heat as possible, with the HP it is all about having minimum run times and keeping the changes in loop flow from affecting the flow through the HP. A double coil tank is good if there is dead water ( solar) on the bottom coil and boiler on the upper coil. I wouldn't use a HP on the upper coil because the flow rates through the HP may not match the needs or performance of the coil. In this case it is better to use an open tank (or single coil) and put a HX on the output for DHW. We also want to avoid using more pumps than we need to so this has to be carefully done.