System design

[crazyquiff]

Hi All,

Been reading on here for a while. As part of our house rebuild I have been working on our heating and hot water system design. I'm looking for any comments (constructive) that anybody might have so I can optimise and get a consensus point of view.

Below are a system and control schematic. Here are some notes on the system.

• Gas boiler is part of a closed loop pressurised system
  Hot water is indirect and has secondary DHW loops - the bronze pump for this is controlled by PIRs in certain zones and overall control on a timer
  Underfloor heating has zoned time and temp controls along with it's own pumps etc (I have ommited the control and distribution of this from the diagram for simplicity)
  Solar thermal input is a closed loop with independant pumps and controls (again not shown)
  All raised temperature pipework is lagged throughout the property
  Not fully decided on both the magnaclean and air separator together
  All gas, electrical and commisioning and sign offs will be done by appropriatle trades
  This work is part of a project requiring building control approval

One of the issues I have not fully bottomed out is the location of the boiler tank stat(s) to maximise the solar input before the boiler kicks in. i.e. in the morning the temp of the heat store will be potentially low and will need a boiler boost, but not so much that the available storage for the solar will be limited. The solar input will be during the day so in the evening the boiler can top up without too much worry about solar capacity. I am thinking of two tank stats run off a two way controller so that in the morning the boiler will top up using a high position stat and in the evening using a lower position stat. I will need to optimise the system (stat temps nd timings) over a period of time to minimise gas use.

I would also like to be able to data log events on the system - if there are any proprietary digital output units out there I would be interested to hear of them. The UFH control system allows this as well as remote control!

Untitled

• crazyquiff
• 2 Jul 2012
• 1

Untitled

• crazyquiff
• 2 Jul 2012
• 1

 

[ALEC1]

Ouch!

 

[Norcon]

Go for an unvented cylinder instead of the thermal store.
Much simpler and more efficient.

 

[crazyquiff]

Go for an unvented cylinder instead of the thermal store.
Much simpler and more efficient.

Apart from the need for a header tank and associated pipework what are the main benefits of unvented over vented? The main benifits I see of the unvented TS is the ability to use the solar for both DHW and UFH and installation cost.

Do you know what the typical efficiency gains are?

I've not found an unvented cylinder that enables all of the inputs and outputs I need. The TS I've identified also allows for a solid fuel or other heat source also.

Cheers

Rich

 

[Norcon]

Do you know what the typical efficiency gains are?

There's nothing documented afaik.
One big advantage is you don't end up with a sludge bucket on your hands.

Also the coil heat exchanger will make your heating system less responsive and is an additional piece of metal that may well give trouble given time.

 

[dcawkwell]

Solar thermal waste of time will never pay for itself.

If you want to go eco forget the gas boiler and go air source with PV electric.

 

[mickyg]

your secondary return looks wrong, would also go unvented, you wont get much heating gain from your solar unless your fitting a half dozen panels or more.
you dont need all the inputs/outputs with an unvented, just a solar coil.
your ufh would come from the boiler.

 

[flameport]

Whole setup is far too complex, you will spend most of the time trying to get it working properly. Data logging ? this is a heating system, not a lab experiment.

Pumped HW circuit - not likely to be required in a house.

Water softener should not be used to supply toilets, which will mean extra pipework will be required for those.

Unvented solar is a bad idea.

Solar is probably a waste of money, as unless you are buying and installing all of it it yourself, it will never cover it's own costs.

Thermal stores - far too much has been said about them already. Search the forum to discover more.

 

[crazyquiff]

@Norcon - hoping to avoid the sludge as the UFH and TS are indirect to the DHW loop. Properly dosed and inert.

Fair point on the heat exchanger - hope that will not be an issue as stainless coil and the UFH is a low temp, slow response system anyway as the floors have thermal mass to them.

@dcawkwell - did look at that as an option but the payback was not there - probably was lowest energy use over the life of the system though. Looked at Ground source also.

@Alec1 - yes they are pricey - half the fun of what I'm doing is to see if I can get a budget system that gets me 90% of the way there.

@mickyg - What's up with the secondary return - is the pump the wrong direction?

The solar is sized correctly I hope! - if not We can add more if needed

"your ufh would come from the boiler." - yes that's the issue and would remove any input from the solar. Comes down to "is the solar sized correctly to the use". I think I will crunch some more numbers on the solar and see where that leads.

I appreciate everyone's input on this

Cheers

Rich

 

[crazyquiff]

@flameport

Yes the system is more complex that your usual run of the mill house install. Datalogging is a way of doing sensible analysis so that you can get the system working at best. Do some analysis - make some changes and then quantify the results. Nowadays there are cheap ways of doing all this.

In our house the secondary DHW is not the be all and end all but as part of the full work adds a small cost so in my view worth doing

Why not use soft wtare in the toilets? to protect the toilet internals?

Unvented solar is a bad idea. Why do you say this?

Our analysis of the solarsystem gives us a 6year payback - time will tell if we get this

Thermal stores - Have done fair bit of research on these - most comments I hear/read for and against are quite subjective so difficult to identify issues.

Thanks for your input

 

[crazyquiff]

@ALEC1 - yes the integration is important. The zone conrrollers are quite sophisticated and take account of seasonal varations etc.

The key part of this for me is balancing boiler and the solar, getting the right energy out to the DHW and UFH. Im not worried so much by the response to the UFH but will need to check again the respose of the DHW (mitigated in part by the secondary loop which acts as mini heat store.

Cheers

Rich

 

[Norcon]

Also keep in mind that when the heating operates, solar energy will be whizzed off to the ufh when it should be contributing to the dhw only.

 

[flameport]

Why not use soft wtare in the toilets? to protect the toilet internals?

Soft water won't damage toilets, but using softened water to flush the toilet is unnecessary waste.
Even in a new house/installation, toilet flushing will still be one of the biggest uses for water.

The result will be that the softener will have to be regenerated far more often, and will therefore use a lot more salt and waste more water, ultimately costing you more money.

Unvented solar is a bad idea. Why do you say this?

Solar panels are a heat source which can't be turned off. Not a good idea to connect one of those to a sealed circuit. Same as not connecting a solid fuel boiler to a sealed system.
When something goes wrong (pump breaks / power failure being the most likely), the sealed circuit will continue to be heated until the whole lot blows up and destroys your house and all those contained within.

Of course, safety valves and other devices would be fitted to a sealed system to prevent this. They would probably prevent disaster.

 

[crazyquiff]

@flameport

Loos - yes that is what I thought - we minimise toilet flush quantity (frequency and volume) and will be using grey water for some of the loos

Solar - unvented - I read your post wrong :doh: - I agree with you, we are planning on the TS to be vented

Thanks to all who have commented - I have a couple more things to verify to check sizing and response times

Cheers

Rich

 

[highleigh]

Your design looks remarkably similar to mine although I havn't drawn it out so very interested to see your plan. I am not putting in dhw, I can't see this is not nessecary for us, I am using radiators upstairs and ufh down so intend using rads that can accept lower temps so I can run them off the ts. I have solar input but will likely add panels later.

Although the system looks complex I too think it can be done on a budget and half the fun is having a system that can be tuned. Interested to hear more about your system. I havn't considered any data logging yet.