Six ensuites with elec showers & just 1 bath. Combi or n

[JohnD]

I stayed in (as it happens an Australian with Solar) a motel where each room had its own small HW cylinder and shower. That meant no single user could have a vast shower and use al the water at the expense of the other guests.

I thought that was a great idea, never seen it anywhere else. I imagine they would have had stand-by immersions as well.

 

[dcawkwell]

Using electric showers would be a mistake.
Do you see a travelodge using electric showers?
You need to keep running costs down and that means gas for cheap
hot water.

As previously stated you need to measure the incoming flow rates
and analyse what demands you may need.

Unvented cylinder(s) and accumulator tank(s) most likely necessary.
Consider acv unvented cylinders very fast reheat times and will
drag as much as the boilers can supply reheating water.

Double glazing. No use getting sentimental.
Wouldn't worry about insulating above the normal.
Zone the rooms so that you can control heating to rooms not in use
and therefore save heating costs.

Thanks DCawkwell. OK, so the message is clear to steer away from 6 electric showers, and whatever way I need to check flow rates and increase pressure as necessary. If I go for a system then, I like the idea of the tank-in-tank ACV cylinders: probably have two for the 5 showers and then perhaps have just 1 electric shower in our area for redundancy.

I was going to put Drayton TRV4s everywhere bar 1 rad, but would I still need to zone?

If I went for a very large combi, I saw a mahusive one that come out very well on the Which? tests, a Worcester Greenstar Highflow 550Cdi. It says it is very good for very large detached houses, or much older period properties with poor insulation; also has low minimum output for heating when needed but has a lot of extra power to heat up rads quickly (7.4 - 29.2kW and 89.2% efficient). However, while hot water heat output is a massive 44kW / 20 litres/min, the water efficiency is just 49% - not sure how expensive this would turn out to be for heating water. Is it worth considering this as a part-combi option?

You should be thinking of two boiler to work in a cascade so you have redundancy should one fail.

 

[indus]

I assume the op is going to have quite massive peak demand? If 4 out of the 6 showers run at the same time you are looking at 50l/minute minimum.

I know his flow and pressure hasn't been revealed but with that sort of demand surely he needs a big break tank and a booster pump?

I don't run a b and b but will be upgrading my system to be able to run three showers in my house at the same time. My plan is to have two large unvented cylinders, two domestic boilers, a 1500l break tank and booster pump

 

[tony101m]

Thanks Indus. What is a break tank and what is an "unvented" cylinder?

 

[Dan Robinson]

A break tank is a large cold water cistern that sits at low level and uses a booster pump to feed the system.

An Unvented cylinder is a pressurised cylinder for hot water.

 

[Agile]

If I went for a very large combi, I saw a mahusive one that come out very well on the Which? tests, a Worcester Greenstar Highflow 550Cdi. It says it is very good for very large detached houses, or much older period properties with poor insulation; also has low minimum output for heating when needed but has a lot of extra power to heat up rads quickly (7.4 - 29.2kW and 89.2% efficient).

However, while hot water heat output is a massive 44kW / 20 litres/min,

So how many showers do you think that 20 li/min will run?

And if the boiler is 19 kW output then where do you think the extra 15 kW comes from?

 

[JohnD]

19?

 

[tony101m]

So how many showers do you think that 20 li/min will run?

And if the boiler is 19 kW output then where do you think the extra 15 kW comes from?

Which? figures not mine, referring to different for heating and hot water. However, convinced not to do combi or electric showers now.

 

[mickyg]

I always think for hotels the "best" solution is water heaters. 3-4 water heaters in parallel means
a) you only heat the water you use, so no wastage at low demand, cheaper to run
b) if one fails you'll probably not even notice let alone cause any issues
c) constant hot water that doesnt run out
d) high flow rate to give multiple outlets good supply

........however.......it also means

a) expensive installation
b) commercial gas supply required
c) potential extra maintenance/service costs.

Stored water from a UV cylinder will probably work out more economical to install and maintain. it all depends on budget.

 

[Agile]

I wrongly typed a boiler power of 19 kW for the Worcs 550Cdi. It should of course be 29 kW.

But its a storage combi and stores a little hot system water. But that only lasts for about 5-6 minutes. Its really designed for filling a bath quickly!

As for 49% efficiency then I dont see where anyone could get that figure from UNLESS its intended to cover a season wide efficiency and take into account the standing losses from keeping the store hot all summer long. The point by point efficiency will be about 90%.

Irrelevant as its not suitable for your needs.

Not mentioned yet but there are some high output instant water heaters by Rinnai which would be a suitable source of hot water for a B&B.

Almost certainly you will need a break tank and pump if you want showers to work together.

But my advice would be to have an unvented hot water cylinder. To do the job properly you will need two at 300 li each! The good news is that they can be heated during the night so you dont need to provide excessive boiler power.

Proper hot water provision is expensive as you will find out.

Tony