Another DIY 'plumber'

[PeterW]

53 minutes ago, Nickfromwales said:

. The temperature and pressure relief valave will be on the uvc factory fitted too, so one less component to buy for the ashp circuit. Just add a filling loop and pressure gauge to the primary heating circuit and your good to go. 

 

@Nickfromwales I’m confused .... the T&P and EV are on the potable side on the UVC, but you suggest you don’t need one on the heating circuit ...???? 

[JIH]

20 hours ago, Nickfromwales said:

If it's a Telford cylinder then go direct to Trevor @ Cylinders2go ( 07939 996940 ) and mention the forum   He'll "quote you happy" ?

I really think you should put the heater inside and just cut the flue hole. Having the heat loss from an LPG unit mounted externally is less than desirable, plus then you do away with the need, and ongoing draining and refreshment, of the antifreeze. Rethink that bit imo, and it'll reduce the pipe work too. 

Yes, the pushfit fittings you linked would be fine. I would use compression immediately around the manifolds though to make things more easily mountable / demountable. The 'iron' reference is just the name for the type of fitting, e.g. goes onto a BSP thread rather than tube, and are typically made from brass. 

For the same sort of money as the cylinder you linked you can get a stainless one from Telford. Lifetime warranty if serviced ( inspected ) annually. That would be an unvented UVC then, and come with all the necessary pressure reducing valves ( PRedV ) and pressure relief valves ( PRV's ), expansion vessel and an immersion heater for back up. The temperature and pressure relief valave will be on the uvc factory fitted too, so one less component to buy for the ashp circuit. Just add a filling loop and pressure gauge to the primary heating circuit and your good to go. 

 

Ok, you've given me some food for thought!  Thanks for the Trevor tip

 

I think I might try this from the other end, so to speak.  I'm settled on using LPG to bring pre-heated water up to desired temperature for DHW.  Therefore I will need a G3 plumber onboard to install it and do subsequent do annual inspections.  I shall see if I can find one to quote for installation of water heater and possibly UCV and annual inspections.

 

If I did decide to keep with the 'vented' option (as per my drawing my understanding) I understand that as long as I don't put in an immersion heater the system is considered to be "used solely for space heating" and the Danger from Heat guidance does not apply (Scottish Domestic Regs 4.9.0).

 

Meanwhile I think I will get Newark to give me couple of quotes, one for a large coil and one for an external heat exchanger and see how it all adds up.

 

Thanks again.

[JIH]

21 hours ago, PeterW said:

 

@Nickfromwales I’m confused .... the T&P and EV are on the potable side on the UVC, but you suggest you don’t need one on the heating circuit ...???? 

 

So if I use the coil side of a UVC for DHW preheat I am using the non-potable side?

[PeterW]

1 hour ago, JIH said:

 

So if I use the coil side of a UVC for DHW preheat I am using the non-potable side?

 

It would be the wrong way to do it. 

 

Having a UVC sat at 45c - or the most you want an ASHP pushing heat out at - is fine. That would need a weekly legionella cycle to take it to 65c but easily done with an immersion. 

 

With the UVC it’s the main body of water that is at mains pressure - a TS has the opposite and does use the coil to preheat. TS is only really useful in this instance if you have multiple heat sources and also use it for buffering for UFH etc. 

 

If you pushed to a 400 litre  UVC with a heat pump coil it’s unlikely you would need the LPG at all - heat to 60c overnight with E7 and a combination of HP and immersion’s and you probably have enough stored hot water for a full day. It removes the complexity of having LPG and the ongoing service and maintenance costs

[Stones]

We have a 300 litre UVC fed by an ASHP. DHW stored at 48 - 49C in the cylinder, fortnightly legionella cycle via immersion. More than enough DHW for a family of four, can easily run 2 showers simultaneously, or run a bath and then a shower and there is still DHW to be had. Returning a CoP of 2.5, so DHW is costing me 5p /kWh. 

 

Forget the LPG, you don't need it, an added capital outlay for little real world gain IMHO.

[Nickfromwales]

On 18/10/2017 at 07:39, PeterW said:

 

@Nickfromwales I’m confused .... the T&P and EV are on the potable side on the UVC, but you suggest you don’t need one on the heating circuit ...???? 

Oopsie. 

I meant they'll come with the uvc as kit, so you can integrate them according to the design. If you buy a dumb vessel then you don't get the package, i.e. no control group, no EV, no PRV etc etc. The uvc comes as a package deal with all the gubbings included in the price. You'll need a few other bits of course but that was what I was trying to get across, poorly.

 

[Nickfromwales]

@JIH

Fyi a 400L HP uvc will come in at around £1100 inc vat and U.K. mainland delivery. A bit less for a 300L and just a few tenners more for a 500L ( as a 400 is made from a cut down 500  ). 

I too was confused at the arrangement, but just assumed ( yes, I know ) that one was a failsafe for the other. 

Also, you can get the uvc with 2 x 3kw or 2 x 6kw immersions for boost / failsafe / backup, which can be used in times of peak DHW consumption eg guests staying etc. ?

[PeterW]

300 litre HP ASHP with additional 3kw immersion (so 2x immersion) was £845 delivered.