Cheap hot water system

[Jilly]

I'm very short of space and money. Solar thermal has had to go out of the window for now. I need to decide re domestic hot water and I'm thinking a simple electric immersion heater is easiest/cheapest, maybe with an electric shower too. I've read about electric combiner's boilers which I'm guessing must be heat on demand type things which look smallish. Does anyone have experience of them? The SAP calc seems to be concerned with timers and insulation. 

 

PS No gas here and still exploring air to air source heat pumps. 

Edited November 16, 2020 by Jilly
addendum

[PeterW]

Electric Combi are the devils work...

 

If you are going DHW via an immersion driven tank then don't bother with an electric shower. Just upsize the tank, and use E7 to give you a decent amount of hot water. Factor in about 80litres of tank capacity at 60c per shower and its not far off. Very little difference with a 210 to a 250 litre tank too

[SteamyTea]

I use a very basic 200lt vented cylinder with two immersion heaters.  The E7 at the bottom and the booster one from the top.

Simple pipework, one up to the feed and expansion tank in the loft, one down from there to the bottom of the cylinder, and another off the top of it for hot water (which also has the expansion/safety pipe that runs up to above the F&E tank.

I fitted a simple electric twin impeller shower pump that needed a pipe from the F&E for the cold side.

 

Simple, very cheap, reliable and once I had insulated the airing cupboard, not mush in the way of thermal losses.

 

You can get this kind of combined cylinder and heat pump.

https://www.earthsaveproducts.com/products/ecocent

But look on Alibaba as the units are bought in from China.

 

There is also a Sunamp if space is very tight.

 

Or even an inline electric water heater, as you have no gas.

 

You say space is tight, do you have space outside?

[SteamyTea]

5 minutes ago, PeterW said:

Factor in about 80litres of tank capacity at 60c per shower and its not far off

Rather a lot, I use about 30 litre of water at 38°C

My 200lt can supply enough for 2 baths and 2 showers, I just turn the temp up to 60°C+

[Oz07]

How long is a normal shower I'm in there 10 to 15 mins

[PeterW]

15 mins at 8-10 litres a minute can use 150 litres. Blended down from 60 degrees, that’s around 55 -60 litres of hot water. Hence the recommendation that you have approx 80 litres per shower as a stored volume. With 2 people I would always size at 210, with a bathroom and en-suite I would up that to 250. If you’ve not got a rapid reheat solution (ie gas or oil) then going one size up makes more sense so 250 would go to 300 etc. 

[Gav_P]

2 minutes ago, PeterW said:

15 mins at 8-10 litres a minute can use 150 litres. Blended down from 60 degrees, that’s around 55 -60 litres of hot water. Hence the recommendation that you have approx 80 litres per shower as a stored volume. With 2 people I would always size at 210, with a bathroom and en-suite I would up that to 250. If you’ve not got a rapid reheat solution (ie gas or oil) then going one size up makes more sense so 250 would go to 300 etc. 

I would completely agree with this... based on my experience, bathroom and en-suite, 2 adults 1 child, we have a 250L cylinder and is fine until we have guests... then we have to plan our showering around reheating time. 

[Jilly]

Yes, loads of outside space.

[Nickfromwales]

1 hour ago, Jilly said:

Yes, loads of outside space.

Do not put it outside!

 

If you absolutely must, and I mean literally no other option is available, then look at a minimum of 300L capacity so you can lower the stored water temperature. That will massively reduce the standing losses from having the tank outside the heated envelope of the house. 
Temperature ( energy ) losses are amplified when the delta between two items is grater, eg tank at 70oC ( off immersion that is likely ) and ambient of 10oC or less will result in major heat loss and costs to replenish. Tank at 50oC in the same situation would have lower losses. 
 

Please put this inside !!

[SteamyTea]

52 minutes ago, Nickfromwales said:

2 hours ago, Jilly said:

Yes, loads of outside space.

Do not put it outside

I should have been a bit clearer for the OCD/Asperger people.

When I say outside, build an 'insulated shed'.

Then plumb in as normal.

This is a thread about getting cheap DHW, not the ultimate installation.

[SteamyTea]

@J1mbo made a comment about HPs and simple vented systems with pumped showers.

Would link to it, but can't seem to do if from my phone.

[J1mbo]

It was just a comment, here: 

 

[Nickfromwales]

8 hours ago, SteamyTea said:

This is a thread about getting cheap DHW, not the ultimate installation.

And a thread where we should give a wide spectrum of information with the various pros / cons / caveats   

If someone is going to buy an UVC then we can advise on the best place to put it, and explain why. 
But, yes, cheap DHW would be an electric shower and a small multipoint, but when you add up all the electrics and the fact that an electric shower is a pile of shit on a good day, an UVC makes sense. Do the sums is my 2-Penney’s worth 

[Cpd]

Can I jump in .... as this thread is about minimal cost hot water systems.... due to living on an island it’s cost prohibitive to get someone in to inspect an expansion vessel on a yearly basis, the cottage that i want to put hot water in is empty at the moment without any plumbing. I wanted to put in an ASHP for UFH and DHW. The building has open vaulted ceilings...... there may be one place to squeeze in a roof tank but it would be within the warm envelope of the house. In this situation what would be my best option. 

 

@Jilly i expect we are in similar situation with a very tight budget .... so I am interested in your solution but I expect you have access to G3 inspection much cheeper than me. 
 

 

 

 

[J1mbo]

One thing that springs to mine with unvented. The risk arises from a depressurization scenario, where the cylinder temperature is over 100*C. Say a fault has resulted in a stored water temp of 120*C at some elevated static pressure. Should the pressure be released, the water will boil and hence expand something like 1600x as steam. This obviously causes an explosion risk.

 

However, an R290 ASHP simply cannot produce water temperatures above 100*C. One because there are multiple protection mechanisms but secondly because it has a critical temperature of 97*C. So there doesn't exist the same risk provided there is no backup heating element as far as I can see.

Edited November 18, 2020 by J1mbo

[ProDave]

10 minutes ago, J1mbo said:

One thing that springs to mine with unvented. The risk arises from a depressurization scenario, where the cylinder temperature is over 100*C. Say a fault has resulted in a stored water temp of 120*C at some elevated static pressure. Should the pressure be released, the water will boil and hence expand something like 1600x as steam. This obviously causes an explosion risk.

 

However, an R290 ASHP simply cannot produce water temperatures above 100*C. One because there are multiple protection mechanisms but secondly because it has a critical temperature of 97*C. So there doesn't exist the same risk provided there is no backup heating element as far as I can see.

The biggest risk of overheating an UVC is an immersion heater with a failed thermostat (which is why they now have a secondary safety cut out as well) but that risk is not unique to UVC's.  Secondary thermostats were mandated after the case of a vented cylinder that had boiled, the venting boiling water had melted the plastic header tank, which ruptured, pouring scalding hot water on a child in a bed in the room below.

 

UVC's have over temperature and over pressure relief valves to protect from over temp and pressure damage, and the control system should be designed to cut off the heat source if it gets too hot.  You are supposed to have a UVC checked annually to ensure these all work.

[PeterW]

29 minutes ago, J1mbo said:

One thing that springs to mine with unvented. The risk arises from a depressurization scenario, where the cylinder temperature is over 100*C. Say a fault has resulted in a stored water temp of 120*C at some elevated static pressure. Should the pressure be released, the water will boil and hence expand something like 1600x as steam. This obviously causes an explosion risk.

Physically not possible. It would require multiple failure scenarios including the failure of all safety systems on the heat input (gas / oil boiler) or immersions on which there are always two;  multiple failures of the control set - bear in mind the expansion of both control block and tank over pressure / over heat would have to fail and they fail to safe; failure of the TMV on the DHW supply mixer. 
 

At that point you would be having a monumentally bad day or someone really didn’t like you .... so I would check your life insurance carefully ! ?

[SteamyTea]

All these 'safety' features add cost and complexity to a system.

 

Mine has a pipe out the top, that then goes into the cold F&E, which can then overflow to the outside.

Now these have failed, and killed people (was a case down here a few years back).

 

I think fitting the thermal fuse to the heating element was a good move, means people need to check out what really went wrong (though re-settable ones are a bad idea).

 

No one commented on my ECOCENT (but find a cheaper version) solution.  I know the newer ones can take heat from outside now, so one down side of them has gone.

[joe90]

25 minutes ago, ProDave said:

vented cylinder that had boiled, the venting boiling water had melted the plastic header tank,

that happened to me many years ago, plastic header tank was about to let go and flood the house. The tank was a funny shape after that. Only noticed it as I heard boiling water sounds from the airing cupboard when walking past.

[joe90]

As a slight “aside” what checks are done on a g3 installation annually? 

[ProDave]

5 minutes ago, joe90 said:

As a slight “aside” what checks are done on a g3 installation annually? 

Basically shut off the incoming water, let the pressure off the HW system. Check the air pressure in the bladder in the expansion vessel (also checking for water leaks)

 

Re pressurise. Check operation of over temp and over pressure blow off valves.  Check water drains freely through tundish to outside vent point, check that is clear and accessible.

 

Run the heating system, check operation of things like the cylinder thermostat and make sure it shuts off the motorised valves etc.

 

There might be a few things I have forgotten.

[SteamyTea]

13 minutes ago, joe90 said:

plastic header tank was about to let go and flood the house

But it didn't.

I think they may make them out of a plastic that has a deformation temperature higher than 100°C now.

Old galvanised tanks did not have this problem,

[joe90]

3 minutes ago, SteamyTea said:

But it didn't.

No, but it was like a plastic bag (this was 40 years ago ?).

[PeterW]

24 minutes ago, ProDave said:

Basically shut off the incoming water, let the pressure off the HW system. Check the air pressure in the bladder in the expansion vessel (also checking for water leaks)

 

Re pressurise. Check operation of over temp and over pressure blow off valves.  Check water drains freely through tundish to outside vent point, check that is clear and accessible.

 

Run the heating system, check operation of things like the cylinder thermostat and make sure it shuts off the motorised valves etc.

 

There might be a few things I have forgotten.

Drain all the hot water from the tank until it’s cold. Start up the heating system and check the temperature cut out operates correctly. 

[SteamyTea]

This problem can be tackled another way: looking at components needed.

 

So a simple vented system has a cylinder, an immersion heater (or 2), a feed and expansion tank, a ballcock valve, couple of isolator valves.

 

What does a unvented system have?