Heat accumulator - Page 3

Solar Mike · 03-13-22, 11:15 PM

Had the same issue when I built my flat plate Solar Hot Water panels and mounted them on the roof, on a cold night the quick lowering of water temperature in the panels would initiate reverse thermo-syphoning out of the hot water cylinder tank.

Fixed by inserting an all brass water swing valve in the line to the panels, place it slightly angled so the weight of the internal valve flap closes fully when the pump has turned off.

Cheers
Mike

Piwoslaw · 03-14-22, 03:21 PM

Quote:

Originally Posted by JRMichler

A simple check valve has a metal disk. The weight of that disk is probably enough to stop convection flow. I suggest just adding a check valve after the pump. I would not use a check valve with a spring because residential hydronic circulating pumps are low head pumps - they create very low pressure. The pressure needed to push the spring open will reduce flow, and could completely stop the flow.

I had a spring-loaded check valve in my spare parts, so I installed it today.
And you were right: The spring is too much for the circulation pump. Even on the highest of the 3 speeds it made strange sounds and hardly moved any water - it barely pulled any hot water out of the tank, after 30-40 minutes the radiators on the ground floor were still cold.

So, I took out the check valve, but did add a heat trap (looping up about 20-30cm above the hot water exit), so I'll see how that works. Its placement is not ideal (after the thermal mixing valve, should be before it), but in the summer I might clean that up and add a non-spring check valve if I decide to add the old tank in parallel.

Piwoslaw · 04-27-22, 02:46 PM

Update.
I read about heat traps and concocted something like this:

The heat trap goes up ~35cm, then down ~20cm, through the pump and up to the radiators. The heat trap is above the mixing valve. Could this be the reason why it doesn't work? The heat still siphons up through the pump and to the radiators

Here is a simple diagram:

During the summer I plan to rework this so that the heat trap is before the mixing valve. Since the low ceiling limits the height if the heat trap goes up above the tank, then can it go down, like this?

If this will work, how low should it go?

Piwoslaw · 09-25-22, 01:05 PM

I made the heat trap which dips almost all the way to the bottom of the tank:

Unfortunately, heat is still being sucked gravitationally from the tank! Only the top of the trap should have been hot, further down it should have been cooler.
But after opening the valves, within a few minutes the whole heat trap and mixing valve were hot, with the heat creeping through the circulation pump up into the house

I'm thinking about that flap valve, as Mike suggested. But must it be mounted so the flow is horizontal, or can it be vertical (so that the weight of the brass flap will hold back the push of gravity-induced flow, like position #2 below)?

Earlier I tried a one-way valve with a disk in it, in position #1, but its spring was too strong and grossly hindered the pump.
After that experience I am afraid that the weight of the brass flap will have a similar effect.

jeff5may · 10-02-22, 09:07 PM

Try putting a heat loop on your return line. If it works, it works.

Solar Mike · 10-04-22, 04:30 PM

Swing flapper valve must be operated with the valve disk vertical, eg whole valve body is horizontal, for low pressure pumps.
To ensure the flapper disk seats correctly I mounted mine at a slight upwards angle from horizontal, my magnetic drive DC pump only draws 1 amp @12 volts so is low power, has plenty of flow through the valve.

Mike

Piwoslaw · 10-05-22, 12:14 PM

Update:
Last weekend I mounted the valve vertically (position #2 a few posts up), so that the weight of the flap holds back the flow when the pump is off. In fact, I even added a few washers to the flap to make it a bit heavier.

It appears that there is enough flow when the pump is on, even when it is at the lowest of 3 speeds. But unfortunately when the pump is off the there is still gravity-induced flow

It might be less than without either the heat trap nor the flap valve, but the whole plumbing stays warm even 20 hours after the pump goes off.

I wonder how much is it that the hot water wants to escape upwards (which the heat trap by itself should already stop), and how much it is the cold, dense water from the house's radiators pushing into the bottom of the tank and forcing the warm water out of the top?

I dunno what else to try

Adding another small washer or 2 to the valve's flap?

I do not want to go in the direction of electrovalves that open when the pump activates, as I want to keep this low-tech.

Quote:

Originally Posted by Solar Mike

Swing flapper valve must be operated with the valve disk vertical, eg whole valve body is horizontal, for low pressure pumps.

Mike, after some reading and thought I believe this would work if I was fighting reverse flow. In my case I have no reason to believe that the flow reverses.
In fact, it keeps flowing even when the pump stops, so I need to eliminate that without hindering flow when the pump is on.

Solar Mike · 10-05-22, 08:37 PM

Perhaps your swing valve is not sealing fully when closed, there must be enough getting past it to keep the water moving.

When the sun goes down and its a clear night, the water in the panels can rapidly cool, with cold water moving back and in turn pulling hot water back out of the cylinder.

Piwoslaw · 10-22-23, 12:16 AM

This summer I reworked the heat trap plumbing on the hot side, extending it first barely above the top of the tank (can't go higher due to low ceiling) then down almost to the cold input:

Hoping this shape, plus the weighted flap of the swing valve, would be enough to stop heat escaping when the pump is not working.

Now that heating season has started I see it didn't stop, the pump and plumbing are still warm/hot, even after a few hours

Only closing the manual valve next to the pump stops the flow, I am afraid that the only solution here might be a mechanical gizmo to open/close the valve whenever the pump is/not powered. I was hoping to avoid that, as I wanted this as simple and passive as possible.

Solar Mike · 10-22-23, 04:37 PM

Makes you wonder how long a heat trap is required, perhaps duplicate what you have and place two next to each other; or add another flapper check valve in the cold line entry into the tank.

Simple solution seems to be getting more complicated. Because you have a powered pump, a simple solenoid valve that is activated whenever the pump is running may be the easiest to implement.

04-27-22, 02:46 PM	#23
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 964 Thanks: 189 Thanked 111 Times in 87 Posts	Update. I read about heat traps and concocted something like this: The heat trap goes up ~35cm, then down ~20cm, through the pump and up to the radiators. The heat trap is above the mixing valve. Could this be the reason why it doesn't work? The heat still siphons up through the pump and to the radiators Here is a simple diagram: During the summer I plan to rework this so that the heat trap is before the mixing valve. Since the low ceiling limits the height if the heat trap goes up above the tank, then can it go down, like this? If this will work, how low should it go? Attached Thumbnails __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

09-25-22, 01:05 PM	#24
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 964 Thanks: 189 Thanked 111 Times in 87 Posts	I made the heat trap which dips almost all the way to the bottom of the tank: Unfortunately, heat is still being sucked gravitationally from the tank! Only the top of the trap should have been hot, further down it should have been cooler. But after opening the valves, within a few minutes the whole heat trap and mixing valve were hot, with the heat creeping through the circulation pump up into the house I'm thinking about that flap valve, as Mike suggested. But must it be mounted so the flow is horizontal, or can it be vertical (so that the weight of the brass flap will hold back the push of gravity-induced flow, like position #2 below)? Earlier I tried a one-way valve with a disk in it, in position #1, but its spring was too strong and grossly hindered the pump. After that experience I am afraid that the weight of the brass flap will have a similar effect. Attached Thumbnails __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

10-22-23, 12:16 AM	#29
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 964 Thanks: 189 Thanked 111 Times in 87 Posts	This summer I reworked the heat trap plumbing on the hot side, extending it first barely above the top of the tank (can't go higher due to low ceiling) then down almost to the cold input: Hoping this shape, plus the weighted flap of the swing valve, would be enough to stop heat escaping when the pump is not working. Now that heating season has started I see it didn't stop, the pump and plumbing are still warm/hot, even after a few hours Only closing the manual valve next to the pump stops the flow, I am afraid that the only solution here might be a mechanical gizmo to open/close the valve whenever the pump is/not powered. I was hoping to avoid that, as I wanted this as simple and passive as possible. Attached Thumbnails __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

03-13-22, 11:15 PM	#21
Solar Mike Helper EcoRenovator Join Date: Apr 2010 Location: Wellington, New Zealand Posts: 61 Thanks: 0 Thanked 6 Times in 5 Posts	Had the same issue when I built my flat plate Solar Hot Water panels and mounted them on the roof, on a cold night the quick lowering of water temperature in the panels would initiate reverse thermo-syphoning out of the hot water cylinder tank. Fixed by inserting an all brass water swing valve in the line to the panels, place it slightly angled so the weight of the internal valve flap closes fully when the pump has turned off. Cheers Mike

10-02-22, 09:07 PM	#25
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Try putting a heat loop on your return line. If it works, it works.

10-04-22, 04:30 PM	#26
Solar Mike Helper EcoRenovator Join Date: Apr 2010 Location: Wellington, New Zealand Posts: 61 Thanks: 0 Thanked 6 Times in 5 Posts	Swing flapper valve must be operated with the valve disk vertical, eg whole valve body is horizontal, for low pressure pumps. To ensure the flapper disk seats correctly I mounted mine at a slight upwards angle from horizontal, my magnetic drive DC pump only draws 1 amp @12 volts so is low power, has plenty of flow through the valve. Mike

10-05-22, 08:37 PM	#28
Solar Mike Helper EcoRenovator Join Date: Apr 2010 Location: Wellington, New Zealand Posts: 61 Thanks: 0 Thanked 6 Times in 5 Posts	Perhaps your swing valve is not sealing fully when closed, there must be enough getting past it to keep the water moving. When the sun goes down and its a clear night, the water in the panels can rapidly cool, with cold water moving back and in turn pulling hot water back out of the cylinder.

10-22-23, 04:37 PM	#30
Solar Mike Helper EcoRenovator Join Date: Apr 2010 Location: Wellington, New Zealand Posts: 61 Thanks: 0 Thanked 6 Times in 5 Posts	Makes you wonder how long a heat trap is required, perhaps duplicate what you have and place two next to each other; or add another flapper check valve in the cold line entry into the tank. Simple solution seems to be getting more complicated. Because you have a powered pump, a simple solenoid valve that is activated whenever the pump is running may be the easiest to implement.