Help speccing a new heating/dhw system

[indus]

Hi there, if you haven't got fed up with me on my previous thread please contribute your expertise/experience.

If you were to design a system for the following requirements what exactly would you recommend? Some of the following already exists, some is being built as we speak and some will hopefully be built once plans accepted

1) Approx 3200 sq ft ( 1600sqft gf, 1200sqft ff, 400sqft loft floor)

2) Four showers (one electric on ground, two non electric on first and two non electric in loft)

3) Two baths, both on first floor

4) Approx 35+ rads.

The house is double glazed at the back but has original single glazed to the front and sides.

I have done a mickey mouse flow test. On the kitchen sink it came out at about 17l/min, when I tested an external tap (ie on the outside wall of the property) it was close to 20l/min

I don't think I'll be able to measure the pressure, so unless you can tell from the flow we'll have to make some assumptions for now.


Every morning AT LEAST two showers need to run at the same time as well as some sinks being filled with hot water. The system needs to be able to handle at least this requirement with ease.

Please assume no space constraints

Thanks in advance for your time and expertise

 

[indus]

Good morning all

 

[Biggles..]

Sorry for the other thread.

What are your heat inputs ie gas boiler,solid fuel,solar etc.

Pressure/flow can easily be sorted by the addition of an accumalator or I prefer the grundfos home booster.

As to go Unvented or thermal store would depend on your heat input.

If it was my spec and free reign I would consider thugs such as separate ch boiler and gas fired water heater like a rinnai,
I'd consider the posibilty of a twin flow.
Normal course for most would be system boiler and Unvented,or 2 separate boilers with one doing heating the other hot water.

Booster set is going to be a must IMHO.

Other things Id be looking to consider would be biomas boiler or solar thermal in view of your large hot water requirement.

Personally I would only advise a thermal store if you were looking into a solid fuel addition,even then I would possibly consider an alternative approach prior to a store/heat bank.

 

[indus]

Sorry for the other thread.

What are your heat inputs ie gas boiler,solid fuel,solar etc.

Pressure/flow can easily be sorted by the addition of an accumalator or I prefer the grundfos home booster.

As to go Unvented or thermal store would depend on your heat input.

If it was my spec and free reign I would consider thugs such as separate ch boiler and gas fired water heater like a rinnai,
I'd consider the posibilty of a twin flow.
Normal course for most would be system boiler and Unvented,or 2 separate boilers with one doing heating the other hot
Booster set is going to be a must IMHO.

Other things Id be looking to consider would be biomas boiler or solar thermal in view of your large hot water requirement.



No probs about the other thread, it's obvious that there is one odd fellow winding up all the other people who are trying to help.

In terms of input I won't be using solid fuel, solar is something I will consider but my area is about to become a conservation area which may cause problems with panel locations?

To be clear, can you confirm the following is your opinion

1) An unvented system would on balance probably suit me better

2) Either use one boiler for ch and one for dhw or consider a separate gas fired dhw heater ie Rinnai

3) With the addition of an accumulator or grundfos booster an unvented system will be possible even if I have pressure/flow issues.

A couple of further questions please?

1) can you tell anything about my flow rates from the numbers I've quoted in the first post or are my measurements too crude?

2) What do you think about the idea of two unvented cylinders being used to cope with the dhw demand. This has been mentioned to me by two companies. Yesterday I went to a friends house who annoyingly is very rich! His house is really huge, I'd estimate 10000 sqft, and he has two Mega Flows.

Many thanks

Personally I would only advise a thermal store if you were looking into a solid fuel addition,even then I would possibly consider an alternative approach prior to a store/heat bank.

 

[Biggles..]

From the measurement you gave your initial dynamic flow figure isn't brill,normally you'd want 20litres plus for any mains hot water regardless if that's through an Unvented or a plate heat.

Unless your showers are set at a max of 8-10 litres each you'll be strugling.

So your options for this are quite simple,increase your service supply pipe size or boost your water.

2 unventeds is massive overkill if sometimes you only use 1 shower you've stored and heated water for 5.

As an alternative suggestion, have a look at stokvis, they do plate heat exchangers that could be a good solution for you.

If you work out probable flow rate that'll be a good starting point ie there will be 3 showers running together with a flow rate of X each.

 

[Norcon]

This is a250 /l oso I fitted in a large 4000sq/ft gaffe a few years ago...

Was recommended by a sales/engineer specifier.
Just an image I snapped part way through the installation.
The dip pipe was removed so about an extra 40/l available.
Its hooked up to four shower rooms and a bathroom.
The mains pressure/flow is substantial and easily runs two showers and two basin taps simontaneously.
Eight people in the property. 45kw oil boiler providing the Ooomf.

And the brains behind it all is one of these....

 

[indus]

Thanks LCG.

In terms of tge flow could tge measurements be affected by some sort of restrictor in the sink tap? The reason I ask is when compared to other peoples house the tge water from my taps seem to gush out
Also I've had my inlet pipe upgraded from the old 15mm lead jobbie so a poor flow seems strange.


Norcon, thanks for the pics. Thats a big house you fitted it in but I don't quite undersrand the maths. With 250litres you won't even be able to run two 10l/min showers for 15 minutes before it runs out of hot water.

Thanks again

 

[Biggles..]

Your showers are blended so 250 litre at 60 is almost 400litres equivalent at 40deg.

It's the flow rate of a mains system that's more the issue with multiple shower/bathroom houses.
You've got circa 20lpm,not brilliant by a long shot,better than most,but won't help you in your finished design.

As you've pointed out, a large store is needed if you like long showers or run the risk of 2 baths after 1 another (average bath 100litres)

 

[Norcon]

It closer to 290/l.
All I know there are no complaints. Not everyone stands in a shower for 15 minutes and also when a 45 kw boiler kicks in the recovery is quite quick.
Also your maths is not quite correct as the hot water @60c is mixed with cold to provide the shower temperature.
Edit. As per lcgs explanation.

 

[Dan Robinson]

Indus, Wise choice to start a new thread - JonasX is no more, for a while at least.


Anyway, The hot water cylinder is stored at 60ish degrees, you shower in the mid 40's. The control system is probably set to top up as it is drawn off, so you are not using all the cylinder's capacity, and that capacity is being at least marginally increased as you go.

I have also in the past used twin coil cylinders with hot water priority control to boost reheat times/running capacity. Although you need a boiler that can keep up.

Nice install there Norcon. What was that Siemens controller? Looked interesting.

 

[Dan Robinson]

Damn - too slow

 

[Norcon]

An RVP 331.

 

[Dan Robinson]

And the pretty panel with lights.... I like lights

 

[dcawkwell]

2 24kw combi boilers (you can use the hot water on demand if you wish
on the ground floor)

2 unvented cylinders split through the building.
Probably 300 litre cold water accumulator.

Boilers central heating linked by header.

 

[Biggles..]

Wow..... Nearly 800-1000 litres or stored water with only 150litres of improved flow through an accumulator.
Use of accumulator not permitted by some unvented manufacturers.

Hope youve firstly got room for 3 very large cylinders and 2 boilers.

I'd definitely be having serious consideration over a stokvis plate heat rig.