DIY Hydronic Floor Heating - Page 17

Drake · 11-02-11, 10:01 PM

Wouldn't one want to have greater heat xfer around exterior walls where heat demand is greatest. Not even heat across floor?

Ko_deZ · 11-03-11, 02:16 AM

That is why the first place the water flows is along outer walls, you make sure to place it like that. Also you make it double, back and fourth, before looping across the floor.then the warmest water will heat along those walls first, which gives you exactly what you ask for :-)

Drake · 11-03-11, 08:25 AM

A floor giving off equal heat along whole surface does not match a space that require more heat around exterior walls, less in interior. Hence radiators or heat vents are best placed along exterior walls. I would think a loop design layout that xfers most of heat first along higher heat demand areas would be best design. Decreasing tubing spacing aroung exterior does the same thing if temp is equal thru tubing.

Ko_deZ · 11-03-11, 10:31 AM

In order to give any heat at all, the temperature of the water must drop trough the loop, that is the only way to get energy from the heated water. If you place the loop as I said, there will more energy released along the outer wall. Browse back in this thread and see AC_hackers pictures if you need to see it visually. Radiators demand a lot higher water temperature, and you will then need separate circuits. Also, heat pumps are less efficient at higher output temperatures. If your floor heating cannot keep a good temperature along the walls and under windows, you would be beyer off by increasing your insulation, and getting better windows.

AC_Hacker · 11-04-11, 10:51 AM

Here are a couple of documents that describe how to determine the optimum size pump for hydronic heating:

TD09 - Understanding Pump Curves

TD10 - Selecting Circulators

These are the clearest explanations I have come across. Because these documents address multiple variables, they may need to be read several times, together, to really 'get it'.

The documents apply not only to hydronic heating, but also to GSHP loop fields and the pumping required there. If I had read and thoroughly understood these documents and the principles they explain before I put in my loop field, I would not be digging up part of my loop field right now.

Best,

-AC_Hacker

pachai · 11-17-11, 01:41 AM

I have been working on the hydronic floor recently,
and today I tested something.
I may not have learned anything.

I have 600' of radiantec 1/2" O2 barrier stapled
under the floor of a 400 SF area. Below is finished,
will be heated soon.

I tested the pipes under the second floor at 80 PSI air.
I did not schlep the compressor up, I did it with a good bike pump. I had tested it at 30PSI and had seen a
bit of loss every day.

It held an hour at 80 PSI, so I connected it
to the hot water tap, let it run until I saw the pipes
at 125 degrees. (I have a Flir Infrared camera).

I shut the OUT to let pressure build,
then after a bit shut the in.

Using the camera, I did not see any statistically
significant difference in temperature where the
pipes ought to be.

I have seen discussions, I gather
the water has to be moving.

I did see a 25 degree (F) difference between the
first pipe in line and the last pipe before the sink.
The heat must be going somewhere (?!)
(125 degrees in, 99 degrees out)

In the bath, there is a loop in the wall for
a future towel rack. It looked like there might
have been a trace of evidence - a 4" strip
that was 2 degrees higher.

I took pics, but it is hours past my bedtime.
Also, phone USB not working.

AC_Hacker · 11-17-11, 01:55 AM

Quote:

Originally Posted by pachai

I have been working on the hydronic floor recently,
and today I tested something.
I may not have learned anything.

Did you use aluminum spreader plates? You really should, it's not too late.

Read this.

If you are not circulating the water (with the boiler firing) you only have a small number of BTUs in the water in your 1/2" pipe. when those BTUs migrate out of the water, they will just warm up the immediate surrounding area.

If you are circulating the water through the pipe with the boiler going, it will constantly supply heat to the floor and this constant supply of heat will work its way up through the floor.

You have a big chunk of floor, so you need a big chunk of heat.

-AC_Hacker

pachai · 11-17-11, 07:32 AM

Quote:

Originally Posted by AC_Hacker

Did you use aluminum spreader plates? You really should, it's not too late.

Thanks, I DID use plates.
I guess the question is, do I really need
the water *moving* to have it give up its heat?
Or is it that it gave up its heat, and I need to
continuously replenish the heat?

I suppose I can test that - by letting the water out
after 5 minutes and see if it is cold.
(BTW, it takes about 2 minutes for
City water pressure to push through 600'
of 1/2" PEX. I'll measure that better next time.
Also, with a bucket, I can measure how much.)

Thanks
Seth

pachai · 11-17-11, 07:34 AM

BTW, at this time, I have no place that I can see
the back of the aluminum plates. Only the pipes going
into the wall and coming back out.

AC_Hacker · 11-17-11, 11:38 AM

Quote:

Originally Posted by pachai

I guess the question is, do I really need
the water *moving* to have it give up its heat?
Or is it that it gave up its heat, and I need to
continuously replenish the heat?

Both.

If you just had a circulation pump and your PEX circuit, and the pipe was filled with water heated up to, say 160F, and you ran the pump, you wouldn't see much difference from what you see now. There's just not that much heat in the water in your circuit.

With a staple-up, even with plates, you'll probably need enough heat to continuously supply a feed temperature of at least 155F.

But if you had a boiler continuously supplying heat into the PEX circuit, your house would get warm.

It's not a matter of moving the water, in your case, it's a matter of continuously supplying heat to the moving water.

The boiler is the heat source, and the water is the conveyor of heat. The conveyor has to be moving to bring the new heat in to replace the heat that has is being absorbed by the house, and ultimately leaks out into space.

The water in the pipes doesn't really hold that much heat, but when you continuously inject heat into that water, your floor will become warm.

Is that clearing things up?

Your house is a big heat sink and it need big heat to get warm.

-AC_Hacker

11-04-11, 10:51 AM	#165
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	Calculating Pump Size for Hydronic Heating... Here are a couple of documents that describe how to determine the optimum size pump for hydronic heating: TD09 - Understanding Pump Curves TD10 - Selecting Circulators These are the clearest explanations I have come across. Because these documents address multiple variables, they may need to be read several times, together, to really 'get it'. The documents apply not only to hydronic heating, but also to GSHP loop fields and the pumping required there. If I had read and thoroughly understood these documents and the principles they explain before I put in my loop field, I would not be digging up part of my loop field right now. Best, -AC_Hacker __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...

11-02-11, 10:01 PM	#161
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	Wouldn't one want to have greater heat xfer around exterior walls where heat demand is greatest. Not even heat across floor?

11-03-11, 02:16 AM	#162
Ko_deZ Helper EcoRenovator Join Date: Jun 2011 Location: Norway Posts: 63 Thanks: 3 Thanked 10 Times in 10 Posts	That is why the first place the water flows is along outer walls, you make sure to place it like that. Also you make it double, back and fourth, before looping across the floor.then the warmest water will heat along those walls first, which gives you exactly what you ask for :-)

11-03-11, 08:25 AM	#163
Drake DIY Guy Join Date: Jan 2011 Location: Mpls,MN Posts: 315 Thanks: 2 Thanked 17 Times in 17 Posts	A floor giving off equal heat along whole surface does not match a space that require more heat around exterior walls, less in interior. Hence radiators or heat vents are best placed along exterior walls. I would think a loop design layout that xfers most of heat first along higher heat demand areas would be best design. Decreasing tubing spacing aroung exterior does the same thing if temp is equal thru tubing.

11-03-11, 10:31 AM	#164
Ko_deZ Helper EcoRenovator Join Date: Jun 2011 Location: Norway Posts: 63 Thanks: 3 Thanked 10 Times in 10 Posts	In order to give any heat at all, the temperature of the water must drop trough the loop, that is the only way to get energy from the heated water. If you place the loop as I said, there will more energy released along the outer wall. Browse back in this thread and see AC_hackers pictures if you need to see it visually. Radiators demand a lot higher water temperature, and you will then need separate circuits. Also, heat pumps are less efficient at higher output temperatures. If your floor heating cannot keep a good temperature along the walls and under windows, you would be beyer off by increasing your insulation, and getting better windows.

11-17-11, 01:41 AM	#166
pachai Renovator-in-planning Join Date: Oct 2010 Location: Northern NJ Posts: 85 Thanks: 6 Thanked 0 Times in 0 Posts	I have been working on the hydronic floor recently, and today I tested something. I may not have learned anything. I have 600' of radiantec 1/2" O2 barrier stapled under the floor of a 400 SF area. Below is finished, will be heated soon. I tested the pipes under the second floor at 80 PSI air. I did not schlep the compressor up, I did it with a good bike pump. I had tested it at 30PSI and had seen a bit of loss every day. It held an hour at 80 PSI, so I connected it to the hot water tap, let it run until I saw the pipes at 125 degrees. (I have a Flir Infrared camera). I shut the OUT to let pressure build, then after a bit shut the in. Using the camera, I did not see any statistically significant difference in temperature where the pipes ought to be. I have seen discussions, I gather the water has to be moving. I did see a 25 degree (F) difference between the first pipe in line and the last pipe before the sink. The heat must be going somewhere (?!) (125 degrees in, 99 degrees out) In the bath, there is a loop in the wall for a future towel rack. It looked like there might have been a trace of evidence - a 4" strip that was 2 degrees higher. I took pics, but it is hours past my bedtime. Also, phone USB not working.

11-17-11, 07:34 AM	#169
pachai Renovator-in-planning Join Date: Oct 2010 Location: Northern NJ Posts: 85 Thanks: 6 Thanked 0 Times in 0 Posts	BTW, at this time, I have no place that I can see the back of the aluminum plates. Only the pipes going into the wall and coming back out.