tegwin
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| posted on 7/2/07 at 11:15 AM |
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OT complicated plumbing issue
Are there any plumbers/heating engineers on here?
I have a complicated problem I need addressing.
We want to connect a pair of air source heatpumps to feed the house radiators and domestic water supply. The most logical way of doing it would be to
use a buffer tank/heat store tank.....
I have done a sketch of how I can visualise it being done, but I am sure there must be a simple way of removing the second domestic hot water tank and
run it all from the heat-store tank..
My god its complicated..maybe I should jhust sod this hightech stuff and get a gas combi...lol
 
Rescued attachment Plumbing schematic GYM 1.JPG
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MikeRJ
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| posted on 7/2/07 at 11:42 AM |
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Many thermal stores use external heat exchangers, so you could use two exchangers one for CH the other for hot water I guess.
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macnab
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| posted on 7/2/07 at 11:54 AM |
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would love to hear from you once fitted on how well it works.
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britishtrident
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| posted on 7/2/07 at 12:25 PM |
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One thing to be aware of is that your domestic hot water storage must be hot enough to pasteurise the water to prevent the risk of Legionella and
other bacteria getting through to showers.
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GeoffT
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| posted on 7/2/07 at 12:33 PM |
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Not sure what sort of tank you intend to use for the 'thermal store tank', but will it withstand pressurised operation? Normal domestic
storage cylinders certainly won't, suspect you've already planned for this though....!
Geoff.
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tegwin
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| posted on 7/2/07 at 12:34 PM |
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Yes, we had thought about the Legionella buggers....
25 years ago we had a enormous air source heatpump installed that fed the house directly...through the radiators and then into the hot water
tank....
Worked great until it packed in...so a year ago we replaced it with an 8KW unit in the same plumbing layout and its been shite!!! Lack of power
mainly I think..
So we are thinking of adding another 12Kw, it would be so much cheaper to just bung another one in next to the first in the current plumbing layout,
but im tolf using a thermal store/buffer tank that it will make the system work better....
Hmmm
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PeterW
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| posted on 7/2/07 at 12:44 PM |
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Tegwin
Easier than you think..! I've got a similar setup, but without the additional input at present.
If you speak to Mark at Newark Cylinders, they will custom build a thermal store to your spec, for not an unreasonable amount of money !
First thing to understand is why do you want to pressurise your rad circuit..? Or the heatpumps for that matter..? Most thermal stores use one or more
indirect coils for 'solar' input, and dump the whole tank volume into the rad circuit when required. DHW heat is via either an internal
heat exchanger coil, or an external plate exchanger. Both have benefits and if you want to know what they are send me a U2U !
One thing you will find is that most heatpumps cannot get to a high enough temperature to provide rad based heating. The temperature deltas just arent
good enough so you will need a secondary heat source to get the store hot enough. Mine runs at 85-90 at the top, 65 at the bottom.
Bear in mind that 20kw is not that much - I'm looking at a 24kw condenser to just get ours running properly, and thats 'instant'
heat from the gas 24x7. Air exchangers will need time to heat that sort of quantity of water.
Why not supplement it with an electric boiler if you already have the power cabling in place..? Something like the
Aztec from Trianco would suit your needs, and provide the required temperatures.
Let me know if you want any further info
Cheers
Peter
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Schrodinger
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| posted on 7/2/07 at 12:53 PM |
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I must admit to not knowing much about the heat exchangers in this sort of system but why would you put an emmersion heater within the heat store?
Surely that would reduce the delta between the source and the store, if you are going to use the heater shouldn't it be in the main tank?
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SixedUp
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| posted on 7/2/07 at 04:37 PM |
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I DIY installed a heat-store last year purely for domestic water. A conventional boiler heats the heat-store up via a coil (to 80c), and then when hot
water is needed, mains-pressure cold water is heated by a 160kw plate heat exchanger using the hot water from the heat-store.
Central heating is provided by the same boiler, and a normal 3 way motorised valve directs water from the boiler to either heat the heat-store or the
radiators or both.
The system works amazingly well, with (in practice) unlimited hot water, delivered at mains pressure. And I only have one tank in the whole house -
the heat-store.
The water in the system is actually divided into 3 completely isolated parts; the sealed boiler/radiators circuit (which has an expansion vessel
attached), the unpressurised heat-store, and the hot water circuit. Since the hot water is just rising main water instantly heated on demand, its
actually safe to drink, so no worries about legionnaires etc.
Now, I see no technical reason why you couldn't also drive the central heating in a similar way (using a plate heat-exchanger), but I think
you'd need a *huge* heat-store to make something like that actually work well, and I don't know enough about the air source heat pumps to
know how they would work with a system like that. Love to know how it works out though.
U2U me if you want more information on what I did, suppliers etc.
Cheers
Richard
[Edited on 7/2/07 by SixedUp]
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MkIndy7
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| posted on 7/2/07 at 06:28 PM |
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If you believe the porblem with the system to be due to the undersized 8kw vessel,
Can you not just simply connect the 2 vessels together.... link the 2 outlets and put a small run around/shunt pump between the two to keep the water
circulating and at even temperatures.
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JoelP
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| posted on 7/2/07 at 07:31 PM |
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what are the benefits of using an air source heat pump? Would a direct heater not be more efficient? I never realised that the idea would work anyway,
assuming that something to do with gibbs free energy would prevent you getting any useful yield.
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tegwin
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| posted on 7/2/07 at 10:35 PM |
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The entire point of the heatpump is that you are getting the heat for free...all you have to do is spend the money to power the pump to collect that
heat rather than paying for the heat and the pump....
We had looked at simply sticking the two units together, but someone recomeneded that it would be more efficient to run them through a thermal store
with an electric boost heater to help bring it up to temp..
I dont know much about heatpumps either and nor do the manufacturor it would appear....
Im at a bit of a loose end really...we paid all this money to get the 8KW installed and it cant cope with 1/3 of the house...let alone the entire
thing, so im not sure what the best course of action is to get the house up to temp....
Dunc
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