Help speccing a new heating/dhw system

[indus]

Thanks to all and for explaining the error in my maths.

Given that I seem to have poor/mediocre flow (which I still find strange as my water seems to gush) it seems you guys are suggesting either an accumulator or home boost pump.

Do you guys have a preference ie accumulator or pump?

And again given my poor flow does it still seem ott to have two unvented cylinders or would two cylinders help in achieving what I want despite the poor flow?

Thanks again, advice greatly appreciated

 

[Dan Robinson]

What Bar pressure is your water main?

If high, then think accumulator or upgrading mains supply.

If low, then a cold water tank pumping through.

Both have benefits and negatives. Lets hope this thread stays objective

 

[indus]

Hi Dan

I don't know the pressure of my main.and don't have the kit or know how to do it. In terms of the mains supply this was upgraded when I had the TS and plumbing done about 4 years ago. .So I don't think there is room for improvement in that dept.

Thanks

 

[Dan Robinson]

The pressure is a vital piece of info.

This is what you need:

http://www.screwfix.com/p/monument-tools-mains-water-pressure-test-gauge/82412

 

[indus]

Thanks Dan.

That item does say 'for washing machines only' in the text. Is it definitely the right one?

 

[Dan Robinson]

Yes mate... it goes onto either the washing machine service valve (think that what they meant - member those catalogue pages are often written by Doreen with a price guide from wherever and very little clue).

It usually fits on an outside tap. it is just a 3/4" nut. You can sue it to measure the dynamic pressure too.

 

[Agile]

As always I have to say its the dynamic flow rate that is relevant.

Something like 10 li/min @ 1.0 Bar PER shower as an absolute minimum.

It always surprises me to read these threads where the owner of a significant house has chosen to dispense with the services of a pro to do the design work.

Thank goodness I missed the thread spoilt by Jonas. ( wasn't there a reference to him in the Bible ? Where Jonas was thrown out of the boat into the sea by the sailors! )

Tony

 

[indus]

Thanks Dan, I'll try and pick one up today.

Tony, I am not dispensing with a pro to do the design at all. There is no way a numpty like me can design this system even with all the fantastic advice offered here.

But this work is going to cost me quite a lot of money (and space) and so I really want to understand the whole process and potential options.

I have two engineers preparing quotes/designs for me as we speak, but this time around I want to understand everything.

That's why I've asked the experts here how they would design the system as this will give me some knowledge to be able to really scrutinise the designs drawn up by my two engineers.

Your input is as always appreciated so don't give up on the thread because you think I'm going about this the wrong way!

Could you kindly tell me how I measure 'dynamic flow rate'?

Many thanks

 

[Agile]

But this work is going to cost me quite a lot of money (and space) and so I really want to understand the whole process and potential options.

Many thanks

Exactly, thats why its so important to get it right the first time.

Search the forum for a description of dynamic flow rate and how to measure it.

It MIGHT be mentioned in the site's FAQ but if so may not be very comprehensive.

Tony

 

[SimonH2]

The biggest problem you have is that there is no such things as the right way to do it. There are many ways, and to a certain extent it's down to preference. As you will have figured from that other thread some people have strong views for/against certain options.

As to "two cylinders", I think that's just a case of them having guesstimated that you need "X" litres of hot water stored, and it's easier to fit two cylinders with X/2 litres each than one big one.

For the size of property, separate heating and hot water may well make sense. Dedicate a boiler to CH, with weather compensation and all that. Then have separate boiler(s) optimised for the hot water.

Then you have a fairly fundamental choice between the options offered - store the DHW in unvented cylinders, or store hot water in cylinders and use PHEs to heat the DHW on demand. The latter gives you the most direct and efficient store reheat as it can be done directly, not via a coil to limit reheat rate (and also force a bottom up reheat). I'm inclined to thing that a well setup cylinder, with direct top-down reheat, and a large PHE will give teh best amount of available hot water for the smallest store - simply because you have continuous high power reheat which means the store only needs to hold the difference between supply and demand over a relatively short period.

You challenge is to find a good engineer who :
a) knows his stuff
b) has the knowledge and openness to consider all options
c) can explain what the appropriate options (note the plural) are, and what the pros and cons of each one are.

IMO, if someone says this is the way to do it then I don't think you've found you man.

 

[Biggles..]

Why look at storing any water.

 

[SimonH2]

Why look at storing any water.

Because, with the peak demand he's got there are questions about the ability to heat it on demand without. That would be something else that needs looking into - what the gas supply can deliver, and whether it would be adequate to heat the water at time of use.

Also, if his required peak demand is higher than the mains will supply, then storage is one way to mitigate that restriction.

Lots of options, lots of variables, lots of "favourite technologies". I don't think his choice is going to be easy !

 

[indus]

Hi Simon

As you say there is no one correct answer, there are many approachs to the issue. I'm trying my best to understand the different methods that can be used and that would be suitable.

Since quite a few people have mentioned a TS with PHE I'm sure it is a very acceptable approach. The thing is neither of the two engineers who I've had around want to do this. They never slagged this approach off, they were very honest and said they weren't used to fitting them.

So the chances are I'll end up with an unvented system as this is what most engineers are used to

 

[SimonH2]

Since quite a few people have mentioned a TS with PHE I'm sure it is a very acceptable approach. The thing is neither of the two engineers who I've had around want to do this. They never slagged this approach off, they were very honest and said they weren't used to fitting them.

So the chances are I'll end up with an unvented system as this is what most engineers are used to

That's part of the problem. There's no denying it that thermal stores and heat banks are not inexpensive (but a heat bank can be made, rather than bought, quite economically), and they have some disadvantages. But then an unvented cylinder also isn't inexpensive either.

The point you raise is probably their biggest handicap. Few are fitted, so few are familiar with them, and so few will recommend them - and some will actively recommend against them no matter what. The upshot is that the majority who aren't familiar with the concepts before they talk to the pros will be steered away from them - and so few are fitted, leading to lack of familiarity, leading to lack of recommendations, and so the cycle continues.

<slight exaggeration alert>And of course, should you break the cycle and fit one, then the next time a jobbing (all the gear, no idea ?) plumber comes along, he'll have a big suck through his teeth and try to persuade you to rip it out, or have a go and botch it up because he won't admit he doesn't understand it*.

* Though I struggle to comprehend how anyone who claims to be a plumber could not understand something as simple as a thermal store

 

[indus]

Since quite a few people have mentioned a TS with PHE I'm sure it is a very acceptable approach. The thing is neither of the two engineers who I've had around want to do this. They never slagged this approach off, they were very honest and said they weren't used to fitting them.

So the chances are I'll end up with an unvented system as this is what most engineers are used to

That's part of the problem. There's no denying it that thermal stores and heat banks are not inexpensive (but a heat bank can be made, rather than bought, quite economically), and they have some disadvantages. But then an unvented cylinder also isn't inexpensive either.

The point you raise is probably their biggest handicap. Few are fitted, so few are familiar with them, and so few will recommend them - and some will actively recommend against them no matter what. The upshot is that the majority who aren't familiar with the concepts before they talk to the pros will be steered away from them - and so few are fitted, leading to lack of familiarity, leading to lack of recommendations, and so the cycle continues.

<slight exaggeration alert>And of course, should you break the cycle and fit one, then the next time a jobbing (all the gear, no idea ?) plumber comes along, he'll have a big suck through his teeth and try to persuade you to rip it out, or have a go and botch it up because he won't admit he doesn't understand it*.

* Though I struggle to comprehend how anyone who claims to be a plumber could not understand something as simple as a thermal store

This is exactly the issue.

Two years ago in December I lost my heating and hot water, it was the very very cold winter when we had record snow and low temps if you recall. My house is 1902 built with part single glazed windows and only partially insulated (at the time)

I called around countless people including BG and NPower, they were so confused by my set up that they were not prepared to venture what the issue actually was. At that time I myself had no idea how my system worked, I had never taken an interest so could not explain it.

Me, my wife and two very small children had the most miserable two weeks of our lives. We were freezing cold and had no hot water. The issue was quite simply that the boiler had failed, but the system confused everybody so much that they couldn't make that call (though one did eventually of course)

That experience was so bad that it has scarred me, I want to have a system that most plumbers inc those that work for BG, the boiler manufacturers etc understand.

Thanks for contributing