Which System?!

[Balenza]

Thanks - Must admit I've been looking at Grundfos alpha pumps, although I'm not sure whether I should go for one for DHW and one for CH or just go for the one (pretty big house!). Suppose I need to spend a bit more time thinking about head heights, volumes and specifications!

Good to know that you think I've got the idea of the thermal store - now I've only got the rest of it to go...

Eh ?. Are you squarepeg in disguise ?.

 

[BigBurner]

Thanks - Must admit I've been looking at Grundfos alpha pumps, although I'm not sure whether I should go for one for DHW and one for CH or just go for the one (pretty big house!). Suppose I need to spend a bit more time thinking about head heights, volumes and specifications!

Good to know that you think I've got the idea of the thermal store - now I've only got the rest of it to go...

Head heights don't matter with a thermal stores. Read up on thermal stores.

 

[Agile]

Thanks again - yes by water tank I mean DHW cylinder. We're probably going to have three bath / shower rooms (one per floor). Mains water pressure is very good (don't know exact pressure, but very high).

One very important aspect you have not mentioned is how many people are going to living there?

Before deciding on the HW system you need to measure the static pressure and the flow rate.

Ideally the dynamic flow rate with the flow rate achieved whilst retaining a dynamic presure of say 1 Bar.

Tony

 

[squarepeg]

Regarding confusion of squarepeg / wobblycogs...

Unfortunately made the mistake of using other halfs pc - auto login as him, not me!

Only 2 people living in the house, but given that its such a large place, we want to future-proof it for others.

 

[squarepeg]

Thinking of a Worcester system boiler (40kW) and a megaflo 300l tank - sealed system. Does this sound sensible?! Thanks again

 

[BigBurner]

Thinking of a Worcester system boiler (40kW) and a megaflo 300l tank - sealed system. Does this sound sensible?! Thanks again

Are you aware of the yearly service charge on Megaflows? You say you want solar. I still go for a thermal store here. It is much better for the CH zoning as no central room stat is needed. You want each zone independent a thermal store will give you that. The thermal store cylinder is a buffer and can inject small amounts of heat to just one zone, while a boiler connected directly onto the radiators will not have a full water flow through the boiler when only one zone is on.

If you for a thermal store then go for a heating boiler and connect it directly, that is not heating through a coil. The CH can be off a coil in the cylinder and have a pressure vessel on it. This mean the cylinder can be vented, along with the boiler and the CH circuit pressurised. This means the cylinder and the radiators can go anywhere in the house.

Have a solar coil in the thermal store, ready for use, and install a few 9kW immersion as well, which makes an electric heating system.

 

[D_Hailsham]

Why have you started another topic asking almost the same questions?

Zoning

 

[Agile]

Thinking of a Worcester system boiler (40kW) and a megaflo 300l tank - sealed system. Does this sound sensible?! Thanks again

That boiler size sounds grossly oversized!

Clearly you have not consulted any professionals for advice on the size of boiler required. When I hear people saying that, I immediately get the impression that its because they think that plumbers are thick and they can easily do it better themselves!

The way to find the size of boiler is by doing heat loss calculations. Most houses need about 12-18 kW !!!

In any case if you are going to have 12 zones then you dont want a 40 kW boiler feeding just one rad! If you are only needing to heat just one room then thats usually cheaper with electricity.

Whilst I dont mind oversizing the HW cylinder as it does not have any negative consequences, 300 li is over twice the recommended size for just two people.

Tony Glazier

 

[squarepeg]

Yes, I agree the boiler size is oversized for two people, however, having done the heat loss calculations we are talking about 26kW on heating alone, (have consulted with several companies). This seems to come down the the fact that the house is big (9 rooms (exclusing baths / hallways and cellar - will be used, and therefore heated) and all are large with high ceilings (smallest is about 3m*3m*2.5m). The house is also old (single glazed, solid brick walls - so no potential for insulation there).

With regards to the size of the hot water tank, although currently only two people live there, it is definitely a familiy house, and although I don't yet have a family I appreciate that accidents can happen! I also feel that while we're putting in a new system, we should make it adequate for the house, rather than for us, as previous history would show that we would be moving on at some stage, and wanting to sell the house (appreciate though that the size of the DHW cylinder isn't most people's first consideration!)

I was therefore considering the 40kW, because allowing 4kW for hot water seems rather measly (loads of people have recommended worcester boilers, and I think the next size down is the 30kW). however, I'm asking for advice, from people who I suspect are mostly highly competent plumbers, because I don't know (and I appreciate I don't have the experience) - so thanks ever so much for your response as I very much value the advice I receive. If you could have a read over this and see if the calculations I've had done still sound excessive, I would greatly appreciate it - (Don't want to spend money unnecessarily!)

 

[Agile]

Yes, I agree the boiler size is oversized for two people, however, having done the heat loss calculations we are talking about 26kW on heating alone,

I've had done still sound excessive, I would greatly appreciate it - (Don't want to spend money unnecessarily!)

How do you come up with a 40 kW boiler by adding 26 kW to 4 kW ???

The recommended allowance for providing hot water is only 2 kW by the way!

The boiler size is not determined by the number of people! Its the heat loss of the house. If yours really needed 26 kW ther that would cost about £200 per week in gas if it was heating at that rate all the time!

Do you really intend to ever heat all the house at the same time?

The number of people determines the volume of stored water. It does not matter oversizing that.

Over sizing the boiler greatly reduces efficiency. Furthermore a 30 kW boiler usually has a minimum heat output of 10 kW. If your heating load is much less that that then that will cause boiler cycling which also reduces efficiency.

I have a friend who is over 60 who had a mistake and now finds he is a father ( again ) when he was looking forward to retirement. His much younger wife is very pleased though.

Tony

 

[squarepeg]

So much for women being good communicators eh! I meant that 26kW on heating only leaves 4kW for hot water on a 30kW boiler, which I didn't realise was about 2x what we need! In that case, it's back down to teh 30kW boiler (thanks, that's just saved me a nice little packet )

As for heating the whole house at the same time - realistically I can't see it happening all that often, but I was under the impression that you should allow for the fact that it might happen... is that stupid?

 

[Agile]

The official amswer is that you should size the heating to be able to heat the whole house because you might sell it next month to a family of eight who will want the whole house heated.

There are two practical factors to be taken into account!

Do you expect to be selling within say five years?

The maximum boiler output is only required when its -1° C outside ! With global warming that hardly ever occurs now! Even if it did you sound unlikely to be needing to heat the whole house. Or you could add an electric heater for a couple of days.

At 0245hrs its still 14.6° C outside here in London and 21.2° C inside and a pressure of 1021 mB.

That implies a nice weekend ahead!

Tony