Converting gravity feed HW to pumped: Where to put the pump.

[damiandixon]

I have an oil fired boiler with two outlets one for central heating which is pumped. The other is gravity feed for the HW.

The HW has a moterised valve.

I want to add a pump to the gravity feed principally to use the HW circuit as a dump for excess heat generated by solar panels. This is to stop the likly-hood of the pressure in the system exceeding 3bar and venting. This kind of occurs when we are away for a few days and we get hot sunny weather.

I am looking at adding a pump on the return pipe near the HW cylindar. Is the siting of the pump sensible? if not where should I try and site the pump?

Is a by-pass loop necessary as the pump should only ever run when the valve is fully open? The boiler only turns on when the valve is fully open or the central heeting is on also the radiator in the bathroom is setup to provide a heat dump when all the valves are closed and the boiler is running.

The controls for the Solar system and a little bit of electronics will ensure that the pump will only run when the value is fully open. I have all the cabling necessary near the cylinder but I don't have access to the solar system relay's near the boiler without running another cable 3 stores.

Thanks
Damian

 

[Agile]

Having just replied to your posting about your solar system I now see that my guess was correct!

Your solar system is obviously wrongly designed or installed or is faulty.

It should stagnate or drainback when the panel temperature gets too high.

Obviously the last thing you want in that situation is to overheat your boiler or hot water or radiators.

It also concerns me that you dont seem to be aware of the dangers which can be caused by overheating water to cause an explosion.

Tony

 

[croydoncorgi]

Your system is VERY dodgy!!!
What happens when the solar panels freeze? (If you're trying to dump heat INTO the DHW, the panels are presumably on the same water circuit as the boiler.)
It sounds as if you need a major rework of the whole thing to make it safe, let alone serviceable!

 

[damiandixon]

The cylinder is a twin coil.

One coil for the solar panels.

One coil for the HW heating from the boiler.

The solar system is closed and contains anti-freeze so should not freeze. As an added precaution if the temperature does drop below freezing then the pump comes on to take some heat from the cylinder.

The system is very standard rather then dodge.

What I want to do is reduce the potential of over-heating. The way that I have suggested is pretty much standard.

However I don't know where the pump should go.

 

[gas4you]

A pressurised solar install should have a safety vent fitted that would open at 6 bar, if I remember correctly, but as said a proper designed system should never have to have this activate.

 

[DP]

You may think you know what you are doing but your post would suggest otherwise. You seem to be overlooking the fact that you have a potential bomb and are tinkering with safety components that could ultimately bring the house down.

Never heard of gravity primary on a solar cylinder.

 

[damiandixon]

Hi Agile,

I saw your other post. This particular system is not meant to drain back when then temperature gets high.

I see you point about the risk of over heating the rest of the system. The solar system is meant to shut down completly when the hot water reaches 90 degrees in the HW tank.

There is an expansion vessile in the loft with a pressure valve set @ 3bar. This is all contained in a large container to capture any water vented.

I think the pressure valve went off when we were away for a week on holiday.

However with the pressure gauge having failed I had not noticed the pressure loss.

The setup is a standard filsol system but using thermomax tubes. It was installed by a registered installer. Having checked the pipe work for leaks it all matches the installation guide.

The only reason I was considering adding a pump in such away is that a friend has a similar system but with a pump added.

During normal use when people are around to use the hot water we very rarely get the tank to reach 65 (well this summer anyway).

I will double check the settings on the controller to see if the settings have alttered (friend's one lost the settings when he had a power cut).

To be honest I would rather not bother adding a pump.

If I can't find any obvious problems I will give the original installers a ring.

Thanks
Damian

Having just replied to your posting about your solar system I now see that my guess was correct!

Your solar system is obviously wrongly designed or installed or is faulty.

It should stagnate or drainback when the panel temperature gets too high.

Obviously the last thing you want in that situation is to overheat your boiler or hot water or radiators.

It also concerns me that you dont seem to be aware of the dangers which can be caused by overheating water to cause an explosion.

Tony

 

[croydoncorgi]

Should have made clear that the objective was to take heat OUT of the DHW cylinder and INTO the boiler and pipework.
Unless you have a REALLY large and old boiler with a VERY large water capacity, I don't see that you'll actually lose much heat that route. And what happens on a REALLY hot day when you got the boiler and DHW primaries up to (say) 85C degrees? Turn off the pump? Carry on regardless of effects of excessive heat on (for a start) the pump itself? You tell me!

 

[damiandixon]

The boiler is a free standing boiler with quite a large water capacity.

The solar controls provide the ability to use the excess heat. I will check with the system manufacture's to see how the system would protect the central heating components from temperatures exceeding 80 degrees.

Either way it looks like the pressure relief value has a very slight weep.

Should have made clear that the objective was to take heat OUT of the DHW cylinder and INTO the boiler and pipework.
Unless you have a REALLY large and old boiler with a VERY large water capacity, I don't see that you'll actually lose much heat that route. And what happens on a REALLY hot day when you got the boiler and DHW primaries up to (say) 85C degrees? Turn off the pump? Carry on regardless of effects of excessive heat on (for a start) the pump itself? You tell me!

 

[Softus]

The system is very standard rather then dodge.
.
.
.
The way that I have suggested is pretty much standard.
.
.
.
However I don't know where the pump should go.

In the standard place.

 

[Sylvan Tieger]

It also concerns me that you dont seem to be aware of the dangers which can be caused by overheating water to cause an explosion.

Tony[/quote]

Tony, are you aware of the American Society of Mechanical Engineers (ASME) or the National Board of boiler Inspectors (NBBI)

According to these codes a low pressure boiler is one defined as 160 PSI or 250 DEGREES F or 15 or less of steam pressure.

Reasonng is in the closed system water expands very little ( that is why we hydrostatically test)

Here is a little known fact

Take a take a balloon fill it up with water POP it and it goes plop quite harmlessly

Take another baloon fill it with air pop it and see the violent reaction happens (called explosion)

Air can be compressed water takes TONS of pressure to compress it

So this lession proves air dangerous water safer.

Heating water above the boiling point in a closed system although not recommended is safer then a lower pressure vapor system

This also explains why you have a RELIEF (liquid) on a boiler set at 30 PSI and on a Safety (vapor) system set at 15#

Of course the ruptured over heated water pipe will flash to steam but the piping itself does not explode it is the medium


Respectifully, Sylvan Tieger certified boiler and unfired pressure vessel inspector and installer

 

[spacethegas]

to all intents & and purposes water cannot be compressed.