Preliminary advice/information regarding hot water supply

[peweuk]

We live in an old 3 bed cottage which is currently serviced by a mains water supply from the local farm. It has a bathroom which is located on the ground floor at the rear of the cottage.
We have an oil fired boiler which supplies radiators for heating, and an old uninsulated hot water cylinder (with jacket).

I am in the process of building a new extension to add 3 more bedrooms and will convert one of the existing bedrooms to an upstairs bathroom.

Locally there is a major building project being planned which will raise a need for accommodation for the workmen for a period of 3 - 4 years, and it was suggested we consider putting en-suite showers in the 3 new bedrooms so they could be used as temporary B&B for the workforce on the new project.

If we do this we need to make sure that we have adequate hot water to allow for the possibility of up to 3 thermostatic mixer showers running at the same time (everyone would be up for breakfast at the same time) as well as general usage of the kitchen sink for breakfast preparation.

So that's the background, now the questions.

Supply:

The incoming water main supply uses a 15mm pipe (crazy I know) and supplies 20 -25 litres/min at 1.5 bar.

We have been advised to install a 50 Gal (220ltr) Break Tank and to feed the house using a pump like the 3CRm80 here ( which will deliver
50 ltrs/min at 2bar or 40ltrs/min at 2.5 bar). This we are told will be an adequate supply.

Storage:

What would be the best solution for storing the hot water to be used by the showers (as well as general use)?

For heating the cylinder we have the choice of 3 different methods.
1. The existing oil boiler
2. Immersion heater
3. An air source heat pump that I have which we are going to install to run underfloor heating in the new extension (some people have suggested this is capable of heating a cylinder to 50 degrees and this should be enough for showering.)

We have the benefit of still having the old separate 'Off Peak' supply to the house which kicks in for 7 hours overnight and the cost of the units makes it an attractive proposition to use either the immersion or Air Source heat Pump to heat the tank overnight.

Question is, what size and type of cylinder would be best to ensure adequate hot water to last long enough for three showers if they were all used at about the same time, and what type of tank would re-heat fastest.
One of these has been suggested.

Sorry for such a long post, but there do not appear to be any plumbers locally who can offer any detailed suggestions, and as I am still at the point of investigating possibilities I am not ready to start taking up the time someone from further afield to come over and discuss the project.

Any thoughts, comments or suggestions would be greatly appreciated.

 

[Bahco]

As you have not yet had a reply I will stick my neck out and say that it may be an unvented system you will need.

Won't be cheap either I'm afraid.

 

[GodKnows]

I agree with bahco, an unvented system with a 300 litre tank fella...

 

[peweuk]

an unvented system with a 300 litre tank

Thanks guys.

I was thinking the same thing myself when I saw this which is the bigger version of the one suggested. At around the £800 - £900 mark that's not too bad

Choosing from the various makes of this type of cylinder could take some research.

However I still have to consider the best/most flexible way to heat the water in the most economical way.

 

[Agile]

I dont think you should be planning to spend a lot of money in the hope of accommodating "workmen" ( I hate that term ) at a UK based B&B rate!

Be aware that some East European workers camp in tents rather than share an overcrowded flat costing them £25 a week.

Its not difficult to design a cheap system.

My suggestion is to use simple electric showers operating directly off the mains.

Even in the unlikely situation that you could get "workmen" to pay you £60 per week to stay with you then what will you do with the extra three bedrooms afterwards?

Tony

 

[peweuk]

Thanks for your concern Agile.

'Workmen' is probably not the right term to use to relate to the people who would be staying as they could be tradesmen, engineers, project managers etc.

However my extension project was planned before the option to offer the B&B option came up, and the 3 extra bedrooms were as much an 'investment' as anything else. As I am building it myself the estimated cost is less than £35,000 (and so far I am under budget), and even with the housing market as it is various surveyors have put an extra £60 - £80K on the value of the property. It has taken me 6 weeks work so far to get to roof plate and the rest of the work I will fit in over the next 6 months.

The project that I mentioned is a major project to extend an already existing major facility, and the sort of people who would be staying will be looking to pay upwards of £30 per night (their allowance is more), so there is a good chance that any investment I make will be recovered over the 2-3 years anyway.

You made a point about electric showers. I thought about that first, but was told that it would be impractical to run 3 'decent' showers at the same time as this would so much power (if all ran at the same time) it could exceed the maximum the Board fuse would take (100A).
For example 3 8KW showers would draw 109A, leaving not room for anything else (such as cooking facilities or heating/lighting etc.)

 

[Agile]

OK well catering for three showers simultaneously is a major project and would need say a 300 litre unvented powered by a pumped system supplied from a 300 litre cistern if you dont want them to run dry.

The advantage of an electric shower is that the capital is so much lower although they will probably need an uprating of your mains supply. Ask the supply co what the current cable could supply as if it does not need to be replaced the cost will be small.

An alternative is to have the room closest to the cottage on the stored system and two electric showers on the further two rooms.

Tony

 

[peweuk]

Thanks Agile.

Interesting suggestion you have made about using a combination of electric and cylinder fed showers, and I will speak to the electricity supplier to check about the supply.

Your other comment about the size of cylinder and feed tank are also interesting.

Taking my two requirements in to account, what you suggest more or less coincides with suggestions I had from 2 different sources.

The first suggestion was to increase the mains pressure by installing a buffer tank filled by the main, and to pump the water in to the house with a pump spec'd to deliver 30ltrs/min at 3bar. A 50gal (227ltr) tank was suggested.

The second suggestion was to install a 300ltr unvented cylinder feeding the 3 showers.

Your suggestion about running 2 electric showers and one off the cylinder may well be a good compromise as it could mean reducing the size of the cylinder (less water heated for times when it wasn't needed) but also means not needing to increase the supply current to accommodate the third shower as the 2 showers would only require 75A, leaving 25A for other facilities.

I now need to work out the cost differences (unit cost plus installation) and consider the practical advantages/disadvantages for each possible solution.

This gives me plenty to think about

 

[Agile]

Forget about the size of cylinder!

There is little difference between the cost of the cylinders to buy.

They are very efficiently insulated so storing more water is no significant disadvantage.

You seem to be undersizing the stored water.

A minimal shower takes about 10 li/min then there are toilets to refill and kitchen water and washing machines etc.

Three 10 min showers use 300 litres without all the other uses. I would say that you need a minimum of 500 li of stored water to cater for longer showers and other water uses!

As I said before, supplying multiple showers at the same time requires considerable resources ( = cost ! ).

Tony

 

[peweuk]

Thanks Agile.

I based the flow requirements having measured the flow volume of our existing thermostatic shower which is about 6ltrs/min (which we personally find adequate flow for a comfortable shower), with the hot and cold being gravity fed from a tank and cistern with no flow restrictors or controllers in the pipework.

However I take your point about the possibility of the breaker tank running dry and was contemplating using a larger tank - not easy to find, but 100gallon (450ltr) are available from Screwfix and we have one of their outlets about 15 miles away.

Usage of 450ltrs with a refill of 300ltrs over the same period, seems about right to allow for the other contingencies you mention, so a 100gall tank will be the way to go.

Thinking about your suggestion regarding electric showers, 3 showers running simultaneously for 15 mins would require 95A and it has been suggested that it may be possible to increase our supply to 200A. All I have to do now is wait for the electricity supplier to come back and tell me if they would be able to increase the incoming supply (they say they need to visit to do a survey), and at what cost.

Once I have all the information I will be able to make a decision about the best solution (cylinder fed, electric or a combination).

Thanks again for your stimulating input.

 

[Agile]

Its most usual to use two 50 gall tanks as thats usually easier to fit in and buy.

That also has the advantage of two ball valves to increase refil rate.

I dont know where you guess your refill rate. Its usually painfully slow and particularly if cold water is being used in the kitchen.

Fitting oversize ball valves will usually considerably increase the refill rate.

Tony

 

[peweuk]

I dont know where you guess your refill rate.

I measured this at an outside tap which is fitted right next to the incoming main. I did it with and without a sink tap open and although it did drop a bit at the outside tap it wasn't much and the 20ltrs/min was the average.

Its most usual to use two 50 gall tanks as thats usually easier to fit in and buy.

I have a store room attached to the back of the utility room where the water main comes in and a 100gal tank and the pump can be fitted there quite easily. However, I take your point about using two ball valves and the oversizing to maximise refill rate.

Thanks again.

 

[Agile]

Flow from an open tap is often FOUR times that from a ball valve.

The orifice in an HP ball valve is usually only about 3 mm !

Tony

 

[peweuk]

Flow from an open tap is often FOUR times that from a ball valve.

Of course it is - So obvious, but I never thought about it. Thanks for reminding me

I wonder if there are any alternatives to a standard ball cock arrangement that would be suitable.

Will have to search around.

 

[Agile]

A low pressure ball valve will usually work OK up to about 1 Bar but is not the official answer but can be a good design bodge! Its difficult to find any design specs for them though. They are just traditional designs which have been made for the last 70 years!

Its these kind of things that someone who has practical knowledge of exactly how things work inside can use to ensure a design performs first time as expected!

Tony