New domestic heating system design advice

[MasterMark]

Lots of useful info here guys, thanks very much. I'll take the Which Local suggestion and see who I can find there. If anyone has any good recommendations for North West London (NW6), feel free to fire away!

Thanks again.

 

[MasterMark]

And forget to say - did a quick test last night and I estimate the flow rate from my taps to be around 15 litres/min. From reading other threads on here that seems to be perfectly adequate?

 

[Agile]

Thats an open pipe flow rate. And not a very good one either! Just about adequate for filling a bath slowly but not much good for a proper shower.

Of course the home booster will give a short duration of good flow and pressure but the poor refill rate will severely limit your concurrent use of water.

The absolute minimum for an unvented cylinder is 22 li/min @ 1.0 Bar

You are still heading for a disaster !

Tony Glazier

 

[MasterMark]

Thanks Tony. It's certainly adequate for my shower at present, but sounds like it won't be if we decide to get those fancy large shower heads. And don't worry, I'll be getting someone in to start doing some proper testing of what we have so we can get a decent system designed.

 

[Dan Robinson]

It also means running more than one outlet at a time us a no no.

 

[BertCoombes]

It is difficult giving advice when not seeing the job. On the snippets read I see three problem areas.

1. I would have a new large bore mains pipe run into the street. This will give adequate water flow for three bathrooms. Of course this must be properly checked and the existing pipe may be fine with a full bore tap on it.

2. As UFH and rads are being used a thermal store is the way. The thermal store can also give high pressure DHW from the mains as well so no need for pumps and Home Boosters. Ensure the thermal store can deliver the flow to the high flow shower heads. If the main is just not good enough consider an cold water mains accumulator rather than a Home Booster.

3. Have the boiler sized properly to heat only the thermal store.

 

[Agile]

"Bert Coombes" sounds just like Dr Drivel/Water Systems/Big Burner who has been banned many times on this site!

 

[BertCoombes]

"Bert Coombes" sounds just like Dr Drivel/Water Systems/Big Burner who has been banned many times on this site!

Someone else wrote that on another thread.

 

[Dan Robinson]

Because it is true.

In a Victorian Flat in London I doubt very much it is feasible to run a new water supply - and even less likely that it alone would supply three bathrooms simultaneously.

In my experience even with a TS, you need to size the boiler to the property.

 

[ALEC1]

it may be difficult to divide an existing supply in a propert, but the ground floor and the lower ground floor could have a new supply from the street...

 

[BertCoombes]

Because it is true.

If you are referring to the ding-bats comments you are his equal.

In a Victorian Flat in London I doubt very much it is feasible to run a new water supply - and even less likely that it alone would supply three bathrooms simultaneously.

In my experience even with a TS, you need to size the boiler to the property.

The flat is a lower ground. It is usually easy to run in a new mains from the street. You have to size a boiler on a thermal store for "average" usage. This means it can be smaller than a boiler heating rads and a cylinder directly.

 

[Dan Robinson]

Yes dear.

And what happens when there is simultaneous heating and hot water draw offs in the dead of winter?

And as for my agreeing with Tony's post... I think the important bit is the one I have taken the liberty of emboldening:

"Bert Coombes" sounds just like Dr Drivel....

Which you do. Simples.

And before you try and be smart a7se back... I am one of the few posters here that DOES like thermal stores. I even have one.... a firking big one at that.

 

[mysteryman]

Thermal stores and condensing boilers are not really compatible with each other. It is far better to have a four pipe boiler with weather compensation; this will cause the boiler to condense as much of the heating season as possible, or all the time if it is underfloor heating.

There have been several other threads on this topic.

 

[BertCoombes]

Thermal stores and condensing boilers are not really compatible with each other. It is far better to have a four pipe boiler with weather compensation; this will cause the boiler to condense as much of the heating season as possible, or all the time if it is underfloor heating.

There have been several other threads on this topic.

It is clear you never took any notice of the threads to come out that untruth. Condensing boilers condense most of running time when reheating a thermal store. Your idea of a 4 pipe boiler will mean the boiler will cycle, efficiency will be impaired by a by-pass valve. With UFH it is best to have only a Geminox that runs down to 0.9kW heat the system. Have DHW separate.

I responded in one thread and here it is:

I registered here to tell people not to use thermal stores for UFH if no more than 10 to 12kW is needed for UFH by using a state of the art very low modulating boiler.

I found many just did not understand thermal stores. Some of the points that come up:

1. They develop sludge.
Some did as they were poorly designed and poorly specified as you stated. Having the CH off a coil in the thermal store cylinder eliminates sludge collection in the cylinder. As it has been mentioned the sludge is just relocated from the rads into the cylinder. A big inspection plate can be on the bottom of the cylinder to remove sludge, but best to have the CH coil to avoid it building up in the first place. Continental makers have domed bottoms so sludge cannot build up and stays in the rads if the system is neglected.

2. They run too hot so are inefficient.
Using an oversized DHW plate heat exchanger gives a lower store temperature and need only be 5 to 10C above the DHW setpoint temperature. If set to 50C then a store temperature of 55-60C will be fine. If a plate heat exchanger send hot water back to the thermal store it is not lost, the heat is still in the store.

3. Condensing boilers do not condense running inefficiently.
This is a fallacy. As Dan has testified, his condenses all the run time. The lack of any cycling greatly increases boiler efficiency.

Some makers refer to their thermal stores as "accumulators", which they are. They accumulate energy in the form of heat.

An advantage of a thermal store is that a smaller, cheaper, boiler sized for "average" use can be fitted. In house extensions a new boiler may not be needed if the existing cylinder is replaced by a thermal store and CH run from the store. In one extension job with an extra bathroom I did this, and fitted a TMV on the boiler return set to 55C to ensure no condensing in the non-condensing boiler. The boiler works more efficiently at lower temperatures and the customer came back and said he is paying no more in gas than he was before the extension.

Hybrid cars and trucks use the accumulator (think thermal store) idea. They use a large battery (accumulator) or hydraulic accumulator as in some trucks to store energy to use for acceleration and claw back braking energy. A largish car running down the motorway at 70mph only needs 20 to 30hp but the engine will be over 100hp and large, heavy, thirsty and expensive. The extra engine hp is for acceleration.

They downsize the engine to give greater efficiency (as you can downside a boiler heating a store) and use the stored energy to boost the acceleration in turning an assisting electric motor or hydraulic motor (think of a thermal store quickly heating up a house on start up with the stored heat). The stored energy in vehicles also evens out power delivery to the wheels (as does a thermal store in using a Smart pump on CH zones). Reclaimed braking energy is stored in the "accumulators" to reuse to propel the vehicle. In some setups, the Vauxhall Ampera come to mind, the charging engine runs at a constant highly efficient speed, or speed range, charging only the accumulator and not driving the wheels (think of a boiler heating only a thermal store with no cycling and No CH connected to it).

If designed and installed properly, thermal stores are the most efficient systems you can have. However, back to my first ever post here. Technical advances in the modulating ranges of boilers and their controls in cases (low temperature UFH) where a store was the ideal choice, that now need not be the case.

Glad to help.

 

[BertCoombes]

A quality condensing boiler with weather compensation, anti-cycling and combustion controls will not short-cycle.

This is 100% incorrect. Few modulate below 5-6kW. If the heating demand is less than this, cycling will occur, which is plainly obvious. Makers say "anti-cycling control", this means a timer before the boiler relights, which is really "cycling delay". Once the system is up to temperature the average UK house will require less than a constant 5kW to maintain the house setpoint temperature. I have given the Geminox that run down to 0.9kW and is the only boiler to go so low, but it is only 10-12kW max, so only suitable for UFH when connected directly. It runs superbly when dedicated to UFH only. No weather compensation needed. Just simple controls you can buy in Screwfix.

When TRVs close down when a house reached temperature the by-pass opens reducing efficiency like a brick. Also these valves are rarely set properly and the springs weaken in time. This is not a problem with thermals store where the boiler runs at optimum efficiency at all times. The bottom of stores can get quite cool indeed, and this cool water gets run into the boiler's return pipe promoting high condensing efficiency.

Connecting the heating load directly to this boiler clearly gives closer control than going via a thermal store.

100% wrong! A CH circuit off a thermal store using TVRs on all rads and a Smart pump gives as low as you want in kW injection into the CH circuit. If the CH only needs 0.25kW it gets it. This is very simple to do and no central electric wall thermostat. All TRVs can close up and the Smart pump automatically stops. Each room has 100% independent temperature control with no central wall stat cut out all the rads.

A conventional cylinder stores water at the required temperature, not at some higher value which will have greater heat losses.

You never read my last post did you? Look at the bit regarding running the store at 60 to 70C. I have run stores at 60C, as the DHW temp was set to 53C. Heat losses? A well insulated cylinder will lose little heat. Buy a cheap cylinder and you may get what you paid for - as with any type of cylinder.

The leading European boiler manufacturer has all the requisite kit available and connectable on a plug-and-play basis.

OpenTherm. Very nice. I like it. But all the control in the world will not eliminate the deficiencies of running rads and a cylinder directly from a boiler that cannot modulate low enough.

A thermal store needs only a very simple non-complicated and smaller boiler. Which tend to be cheaper and far more reliable. As I have written, I have seen thermal stores with simple boilers running on them perfectly after 28 years. The boiler will go another 15 years by the look of them. Thermal stores are kind to boilers.