Building Regs and replacing vented cylinder with Heat Bank

[SumoAl]

I am going to replace my standard DHW cylinder with a DPS GXV mainly as a buffer tank for the central heating as I have a non-modulating boiler with Honeywell CM-Zone gear on all radiators (with automatic bypass to keep boiler flow going) and it's just not working well at the moment.

I was thinking of doing this myself, I've done other CH and mains and DHW stuff before and putting the heat bank in doesn't concern me greatly. They are not the most complex of things to work with.

However I am confused as to what I need to do with regards the building regulations. Do I need to inform Building Control that I'm doing this? If I get someone in to do it can they sign it off instead of Building Control? Any approved person type registrations I should be looking for?

My local Building Control department told me on the phone I don't need to inform them, but I'm not sure the receptionist knew what I was talking about. Could just run with that, but I doubt if that will help much if I should have got approval for it.

Thanks.

 

[Dan Robinson]

I can't see why BC would need to be told about this as you are not altering the gas side of things, nor installing an unvented cylinder.

Not too sure whether you need to go to such lengths just because "it's just not working well at the moment"; but then we don't know the history.

 

[SumoAl]

Bit of background:

I have a standard Worcester 19/24cbi boiler pumped to nine radiators and a kitchen plinth heater. All radiators have TRV bodies with Honeywell CM-Zone HR80UK controllers and the plinth heater has a two port valve on it for flow control. As everything could be shut there is an automatic bypass to keep the boiler flow going.

This means that we could have one radiator partially open being driven by a 24KW boiler pushed around by a Grundfos 15-50 pump with most of the water going through the bypass. Very inefficient way of running things. With the CM-Zone system this can happen a lot of the time, in fact most of the time there may only be one or two rooms that need heating, they get satisfied then another room gets a bit cold and kicks it in again etc etc.

So I was going to add a buffer tank to allow the boiler to fire at full power and allow a modulating pump to pump water around the central heating system. The only place to put it is where the current vented DHW tank is, the airing cupboard on the ground floor, so I need to provision DHW as well from the buffer tank. Heat bank fits the bill.

That's the thought train so far. I've been playing with Panex (the DPS Flash tool) for a while and quite like the sound of the GXV, the theory sounds good and it's low tech enough to maintain easily. Maybe I've jumped a bit quick into this conclusion but it does appear sound.

Or should I be thinking down a different line of attack. The idea is to reduce the amount of time the boiler is running with very little of the heat doing anything useful.

 

[Dan Robinson]

Sounds like an awful lot of work and material outlay for naff all practical gain to me.

 

[Doctor Drivel]

Sounds like an awful lot of work and material outlay for naff all practical gain to me.

Are you drunk?

He wants:

1. A buffer to improve the performance of his boiler - no cycling.

2. A CH circuit with a modulating pump (Grundfos Alpha type) and eliminate a wall stat and have TRVs on all rads (I assume)

3. A neutral point.

He looks around and sees heat banks and they also give high pressure DHW as well.

He is onto a winner here and a lot of gain.

 

[Dan Robinson]

ooookkkkaaaaayyyyyy then.....

 

[htgeng]

ooookkkkaaaaayyyyyy then.....

You know I often wonder if DD invents new users to post these 'questions' on heatbanks etc. Most postings are from relatively new users and have very similar dialogue. hmmmm shame diynot doesn't log posting IP's

 

[Dan Robinson]

Not that I really give two runny shlts, but he doesn't do the idea of Heat Banks or Thermal stores any good. Hell its nto even as if most regualrs here autimatically opt for an anti-thermal store approach. I have 2 jobs on drawing board now that MIGHT benfit from a heat bank arrangement.

Assuming for a brief moment he isn't sad enough to make multiple identities; the very fact that he only seems to pop up now and then when a thermal store issue MIGHT arise is odd in itself. A bit like a certain other poster who only seems to appear for specific reasons.

 

[croydoncorgi]

Maybe the OP (or DD!!)can explain why the HC60NG demand unit can't be used to solve the cycling problem. Much smaller and presumably a lot cheaper......

 

[Dan Robinson]

So you read the manual as well then .

 

[croydoncorgi]

What manual?
It's even on the datasheet!

 

[SumoAl]

Based on my experience as an end user having to live with a CM-Zone system.....

The problem with the HC60NG (which I have two off, one as a zone control for the plinth heater and one for the boiler control) is that they do what they are told.

They cycle on 12/6/3 cycles per hour so either 5/10 or 20 minute long cycles. They are on for a proportion of that cycle depending upon demand which is done on difference between current and ideal temperature.

So you can end up with the situation where the HR80UK (TRV motor unit) has the trv valve partially open with short demand (say 5 of 20 minutes). Because most of the water goes through the bypass and not through the radiator circuit it means that the (quite long) run between boiler and the airing cupboard which houses all of the valves heats up and just abouts manages to start to heat the radiator when it gets turned off for 15 minutes.

The water in the radiator circuit then cools down so when the next cycle starts we are back to square one.

I had this happening most of the night at one point which means that lots of electricity and gas is being consumed to heat up the bypass circuit and not much else.

Sooooo, I thought buffer tank, no bypass, modulating pump in constant pressure mode.

Came on here to ask about building regs as I wasn't sure.

Can someone answer that question with a definitive answer please.

Thank you.

 

[Dan Robinson]

Think I covered that in my first post...

 

[croydoncorgi]

To answer your first (and direct) question:

heatstores are nothing to do with Building Regs Part G3, which relates only to pressurised DHW systems with volumes greater than 15 litres.

However....
If you want to create an efficient system involving an HE condensing boiler and a heatstore, you need to be careful about minimised Return temperature (<56 degrees). DPS has a blender on the Return from the store exactly for that purpose.

I'm intrigued by your problems with the Honeywell CM-Zone system, particularly the HC60NG thing. I'm really surprised that Honeywell has got the internal control logic so wrong that it gets into the situation you describe. OK - it's only a relatively simple gadget but from your description of it's timed-on periods, it sounds like a problem waiting to happen!

 

[Dan Robinson]

My two CM systems work beuatifully - CMZone on the rads, CM67NG on the underfloor; which as it happens, also also a plinth heater connected in series on the return.

Boiler doesn't cylcle that much at all (then it does work as a kind of heat bank I suppose).