Wanting to reduce gas usage - New Heating Design Circuit - will it work?

Freepost

Solarchaser said:

For me looking at your proposed system, and mine as it is, I look at it as 3 separate circuits. 
1. The tank water/boiler
2. Central heating
3. Potable water

So keeping them separate would require two coils, but if you want to have the boiler and potable water together, fair enough, my thoughts on the tank is that its essentially dirty water, but its designed for it to be potable, so you can obviously use it as such.
My only concern would be if you were running the tank from solar for 6 months of the year say, then the water in the boiler and in the pipes would not move, this would be stagnant water and ripe for bacterial growth, so you wouldn't want to be drinking it, but most people won't be drinking hot water anyway.... in the back of my mind is the kids doing their teeth in the winter will probably blend in a bit of hot water.
You could probably negate this by running the boiler for say an hour a week, but for me, I wanted there to be as little chance as possible of any bacteria in the hot water, and a coil in very hot water does this.

Hi Solarchaser,

It's possible that I have misled you, what I was proposing was for the water in the tank, used for DHW, to be heated indirectly by the system boiler. This would result in a two coil system, comprising of a bottom coil for the system boiler and top coil for central heating.

Of course the original idea was for a three coil system, from top to bottom, Central Heating Coil, DHW Coil and System Boiler Coil but perhaps the System Boiler Coil isn’t necessary and could be connected directly between the System Boiler and the Tank.

An alternative, could be a one coil system where the system boiler is connected directly to the tank and the contents of the tank is used to provide central heating directly, the only coil in the top of the tank, being used to provide DHW. I'm not too sure that I like this idea!

I’ve contacted Cylinders to Go to ask for a price and lead time for a 500l two coil system.

Thanks for your help.

F.

michaels

Freepost said:

Solarchaser said:

For me looking at your proposed system, and mine as it is, I look at it as 3 separate circuits. 
1. The tank water/boiler
2. Central heating
3. Potable water

So keeping them separate would require two coils, but if you want to have the boiler and potable water together, fair enough, my thoughts on the tank is that its essentially dirty water, but its designed for it to be potable, so you can obviously use it as such.
My only concern would be if you were running the tank from solar for 6 months of the year say, then the water in the boiler and in the pipes would not move, this would be stagnant water and ripe for bacterial growth, so you wouldn't want to be drinking it, but most people won't be drinking hot water anyway.... in the back of my mind is the kids doing their teeth in the winter will probably blend in a bit of hot water.
You could probably negate this by running the boiler for say an hour a week, but for me, I wanted there to be as little chance as possible of any bacteria in the hot water, and a coil in very hot water does this.

Hi Solarchaser,

It's possible that I have misled you, what I was proposing was for the water in the tank, used for DHW, to be heated indirectly by the system boiler. This would result in a two coil system, comprising of a bottom coil for the system boiler and top coil for central heating.

Of course the original idea was for a three coil system, from top to bottom, Central Heating Coil, DHW Coil and System Boiler Coil but perhaps the System Boiler Coil isn’t necessary and could be connected directly between the System Boiler and the Tank.

An alternative, could be a one coil system where the system boiler is connected directly to the tank and the contents of the tank is used to provide central heating directly, the only coil in the top of the tank, being used to provide DHW. I'm not too sure that I like this idea!

I’ve contacted Cylinders to Go to ask for a price and lead time for a 500l two coil system.

Thanks for your help.

F.

Would the single coil be to prevent 'dirty' water going through the plate heat exchanger?  Basically this is then a second heat exchanger in the tank so you have to factor in how quickly it can transfer heat.  It would want to be at the top of the tank to maximise use of the warmest water.

michaels

EricMears said:

michaels said:

I remembered who supplied our cylinder, DPS Heatweb.  Unfortunately they don't seem to be around anymore and the engineering drawings of the tank plus heat exchanger were on their webportal so also no longer accessible.  Apologies.

Still seem to be at https://www.heatweb.co.uk

Thanks,  I found some old (15+ year old) emails and the links in them took me to what is obviously now a previous version of their website that had an adobe flash powered configurator that no longer works so I assumed they were no longer around.  They probably need to take the old website down and redirect to the new one....

Freepost

michaels said:

Freepost said:

Solarchaser said:

For me looking at your proposed system, and mine as it is, I look at it as 3 separate circuits. 
1. The tank water/boiler
2. Central heating
3. Potable water

So keeping them separate would require two coils, but if you want to have the boiler and potable water together, fair enough, my thoughts on the tank is that its essentially dirty water, but its designed for it to be potable, so you can obviously use it as such.
My only concern would be if you were running the tank from solar for 6 months of the year say, then the water in the boiler and in the pipes would not move, this would be stagnant water and ripe for bacterial growth, so you wouldn't want to be drinking it, but most people won't be drinking hot water anyway.... in the back of my mind is the kids doing their teeth in the winter will probably blend in a bit of hot water.
You could probably negate this by running the boiler for say an hour a week, but for me, I wanted there to be as little chance as possible of any bacteria in the hot water, and a coil in very hot water does this.

Hi Solarchaser,

It's possible that I have misled you, what I was proposing was for the water in the tank, used for DHW, to be heated indirectly by the system boiler. This would result in a two coil system, comprising of a bottom coil for the system boiler and top coil for central heating.

Of course the original idea was for a three coil system, from top to bottom, Central Heating Coil, DHW Coil and System Boiler Coil but perhaps the System Boiler Coil isn’t necessary and could be connected directly between the System Boiler and the Tank.

An alternative, could be a one coil system where the system boiler is connected directly to the tank and the contents of the tank is used to provide central heating directly, the only coil in the top of the tank, being used to provide DHW. I'm not too sure that I like this idea!

I’ve contacted Cylinders to Go to ask for a price and lead time for a 500l two coil system.

Thanks for your help.

F.

Would the single coil be to prevent 'dirty' water going through the plate heat exchanger?  Basically this is then a second heat exchanger in the tank so you have to factor in how quickly it can transfer heat.  It would want to be at the top of the tank to maximise use of the warmest water.

Hi Michaels,

The discussion with Solarchaser had gone away from using Plate Heat Exchangers to using coils within the tank, the argument being less joints to leak and less equipment to fail.

Thank you for your input and best regards

F.

markin

I think you both under sized it a little.

https://www.youtube.com/watch?v=D5mznXjkhQM

Solarchaser

Feels a bit like a mick Dundee "that's not a tank.... thats a tank"

Freepost

Solarchaser said:

Feels a bit like a mick Dundee "that's not a tank.... thats a tank"

I remember the film(s) really good, Paul Hogan could certainly deliver the line, his timing was excellent.

But back to the tank, I have spoke to your contact and he proposes a single coil, with the coil towards the top of the tank for DHW and the boiler to be directly connected to the tank together with the central heating, the problem is that it seems an immensely expensive solution when compared with the Plate Heat Exchangers. May I ask what model of tank is yours ... 500l Tempest (horizontal)?

Thanks

F

Solarchaser

Yeah its a 500L tempest horizontal, though he said it's not technically a tempest because it's custom. 
I think mine was around £1600, so yeah definitely not cheap.
A quick Google says the same place does a twin coil t00l for £1300, but then another for £1800 and I don't see the difference, perhaps larger or longer coils ??

With my system I want to forget about it largely, and thermal loss is a big issue because the tanks are not in my home envelope. 
It's probably much less of an issue for you if the cylinder is vertical and in an accessible area within your envelope.

I initially looked at plate exchangers, and went as far as very very almost buying two nordic ones similar to this, but only 30kw
https://www.ebay.co.uk/itm/194386376049?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=KFK6JG88SyC&sssrc=2349624&ssuid=DtbsXk1pRsq&var=494500444722&widget_ver=artemis&media=COPY

However for me, when I started adding up the price of heat exchangers plus the pumps plus the logic to run them, it looked pretty much cost neutral I decided it was better for my purposes to have the least possible external parts and least possible mechanical parts.

You obviously have to go with what you think.

70sbudgie

markin said:

I think you both under sized it a little.

https://www.youtube.com/watch?v=D5mznXjkhQM

This was really interesting, thank you!

Reed_Richards

I'm late to this conversation but I have a pumped loop feeding my hot taps so I can give you some observations.

1. I run the pump for 5 minutes every hour except when we are asleep.  This keeps the water in the loop adequately hot except in the middle of the night.
2. It took a bit of searching to find a timer that would allow me to run the pump 17 times a day for 5 minutes each time.  Electromechanical timers did not work properly but I eventually found an electronic one.
3. My loop splits in two so each half has a valve on the return which shuts down the flow once it reaches a certain temperature (being the temperature which I want my water to be).
4. My circulation pump (later on the return) also cuts the flow once the water passing though it reaches a certain temperature.  This is belt and braces.
5. In my case the flow is the output from the cylinder and the return goes to the secondary return port on the cylinder.  There is a TMV on the output.  This is not the ideal plumbing arrangement but it works except in summer.
6. In summer the tank can get very hot, 65 C or a bit more, because I heat it with spare solar power.  In principle this could lead to a scalding risk because the hot water won't get mixed until a tap is open so the loop might fill with scalding water.  What actually happens is that loop fails to circulate anything more than tepid water.  This is less than ideal but in summer you don't mind so much.  I presume this happens because the TMV can't cope so just shuts down the flow.