New electric water heater only producing luke warm water......HELP!!

[sammathias]

Any help would be much appreciated!! installed two Heatrae Sadia 7.0kW MultiPoint Instantaneous Water heater in parallel to feed a bathroom today, when i came to commision heaters they only produced luke warm water even after regulation the water flow.
instantly i thought one of the heaters was faulty and only delivering cold water which was cooling down the hot water from the other heater, this wasnt the case as i tested the heaters seperatly with the same results. Its hard to believe that the stats on both heaters are faulty on new heaters, any suggestions??

 

[SimonG]

Watts equals amps x volts

14000 = 60amps x 230

With other stuff in the house I'm surprised you didn't blow the suppliers fuse.

 

[sammathias]

Clueless, got a sparkey to wire the heaters up. would it be the wiring causing the water not to heat?

 

[lbp plg & htg]

Any help would be much appreciated!! installed two Heatrae Sadia 7.0kW MultiPoint Instantaneous Water heater in parallel to feed a bathroom today, when i came to commision heaters they only produced luke warm water even after regulation the water flow.
instantly i thought one of the heaters was faulty and only delivering cold water which was cooling down the hot water from the other heater, this wasnt the case as i tested the heaters seperatly with the same results. Its hard to believe that the stats on both heaters are faulty on new heaters, any suggestions??

Really??? 7kW?? Each??

 

[Ray Stafford]

Any help would be much appreciated!! installed two Heatrae Sadia 7.0kW MultiPoint Instantaneous Water heater in parallel to feed a bathroom today, when i came to commision heaters they only produced luke warm water even after regulation the water flow.
instantly i thought one of the heaters was faulty and only delivering cold water which was cooling down the hot water from the other heater, this wasnt the case as i tested the heaters seperatly with the same results. Its hard to believe that the stats on both heaters are faulty on new heaters, any suggestions??

Hi Sammathias

It sounds like a design problem to me.

Compare it with something we are all used to. Lets say you had a 28kw combi feeding the bathroom. You would expect maybe 11 litres a minute at a temp rise of 35 deg C?

That would be fine for a basin, but the bath tap might need throttling back a bit. At this time of year, with a low incoming cold main temperature, it might struggle a bit, but most installers would probably say a 28kw combi was just about barely adequate for an entry-level system.

You don't have 28kw, you have 14kw. Therefore, you are either going to get half the flow, or half the temp rise. Theoretically you need to throttle back the flow to an unacceptably low level to get hot water at a decent temperature. At anything like an acceptable flow rate, the temperature rise is only going to be ~18degC.

You would need 4 of those babies to approximate to the output of a cheap gas combi, and as other posters have pointed out, that would mean an industrial upgrade to the electrical infrastructure, and in use the leccy meter would spin like a top.

I'm assuming there is no gas in the property? Is there room to fit a small direct unvented cylinder somewhere? Other than a single point shower, electric water heating really needs storage of some sort.

 

[lbp plg & htg]

Like I said previous - 7kW?

3, 4.5 but 7?

 

[Ray Stafford]

Like I said previous - 7kW?

3, 4.5 but 7?

I think he has two of these. Link

 

[lbp plg & htg]

Still surprises me how they add upto 7Kw though. I'd like to know more about the set up, sizes, kilowatt ratings before being able to offer more advice.

 

[sammathias]

Basically they have an indirect system present with a lpg system boiler. They have electric showers in all bathrooms and dont believe in heating the cylinder to produce hot water for the basins, sink and bath. even after throttling back even after throttling back the flow the temperature didnt rise above 10 degrees. yeah the heaters are both 7kw and the link provided by ray is correct. needing a 28kw boiler personally is over sized. maybe 14kw is too low. will see if they want to add another heater, should still be above 10c with 2 tho?

 

[sammathias]

ohh and ray, INDUSTRIAL electrics for a domestic property???? sorry im no sparkey, seems like i need to educate him tho?????

 

[Ray Stafford]

ohh and ray, INDUSTRIAL electrics for a domestic property???? sorry im no sparkey, seems like i need to educate him tho?????

I'm not a sparky either, but if you add a 3rd 7kw heater, thats a big load for a domestic installation. 91 amps on my calculator.



Going back to your design, you have 14kw at present, and a watt will raise 1 litre of water by 1 degree C in one hour.

Assuming a desired temp rise of 35 degree C, your max flow rate is 14000/60/35 = 6.66 ltrs per min. Thats in a theoretical perfect world with no inefficiencies and no losses to pipework etc. In reality, I guess that about 5.5 litres/min is about all you will get. Thats poor at a basin or sink, and woefully inadequate for a bath. As scale builds up on the elements, that performance will drop further.

I have to say that I think your clients are chasing a false economy.

 

[sammathias]

Yes, 30a each if i can remember. i still would have expected decent heat at a basin tap from the two heaters, giving say an electric shower is 9.5kw and at full heat its hard to hold your hand under. maybe i should drill it into the client that it isnt going to work, even tho he is adament two is enough.

 

[Ray Stafford]

Yes, 30a each if i can remember. i still would have expected decent heat at a basin tap from the two heaters, giving say an electric shower is 9.5kw and at full heat its hard to hold your hand under. maybe i should drill it into the client that it isnt going to work, even tho he is adament two is enough.

Yep, but the flow rate would be awful. Page 8 of this link gives the flow rate graph for a Mira Vie shower. At 35 degree rise, the flow rate of a 9.5kw model is only about 3.5 litres per minute. To get it blazing hot, with a really cold incoming main would mean a flow rate of between 2 and 3 litres per minute.

If you tried to fill a bath with an electric shower, it would take so long that by the time it was full, the first few litres of water would be cold anyway.

 

[Ray Stafford]

Something else for your client to consider:

According to this source the cost per kwh for electricity on standard tariff is 15.69p. The cost per kwh for LPG is 8.17p - just over half the price.

Assuming a properly insulated cylinder and sensible controls, I would be surprised if stored hot water was only 50% efficient. Ok, there are some losses, but surely not that much?

 

[tamz]

They have electric showers in all bathrooms + the heaters are both 7kw

I hope your spark is well clued up. You will need contactors fitted to control this lot. If they are wired direct, unless it is a 3 phase supply it will overload.

Basically they have an indirect system present with a lpg system boiler. and dont believe in heating the cylinder to produce hot water for the basins, sink and bath.

Something made up like this would work better
No shower pump required - YouTube

 

[lbp plg & htg]

I think he has two of these. Link

Your correct Ray with the design problem. These have been based on the backplate of the old Santon Powerpack (7 &9kW) which at best would suffice a small bedsit - shower whb but not much more. A clamp meter on the live from each would confirm that units are working to spec and and a resistance check across the terminals would also confirm it but you never going to get more than 7kW of heat whether in series or parallel.

Unvented cylinder has to be the way forward.

 

[lbp plg & htg]

Really??? 7kW?? Each??

Must apologise sammathias - i was only recently speaking to r&d at Heatrae not long ago about new products and he never mentioned these were out on the market. They are also available in 12kW but as Ray has previously mentioned you would be better off with a cylinder depending on what the purpose they are required for.