Hot water cyclinder in loft

shibli

Hi

I have a unvented 250 ltr hot water cyclinder located in the loft next to the system boiler which is programmed to heat the water 30 mins in the morning and again late in the  afternoon at 60c. The issue I am finding is by early afternoon and late in the evening the water isn't as hot heat and sometimes requires a boost. I was thinking the loft is a cold place so that likely cools down the cyclinder and the copper/plastic pipes flowing in and out of the cyclinder after some duration. Would it help if lagging the pipes retain more of the heat in the pipes/cylinder ?

TIA

Screwdriva

1) If your tank is a copper tank, insulate it. If it’s a modern cylinder then it is already well insulted. 

2) Ensure you have insulated all hot pipes going into and exiting the tank with reflective thick pipe lagging.

3) Have your plumber visit and check for cold water mixing to the cylinder. This is where a faulty shower valve can leak cold water into the return pipes constantly, diluting the hot water within the cylinder. This is far more common than people realize and a reliable indicator is the need to recharge the cylinder often despite low usage of hot water (3 showers or less in between recharges as an example).

Once these are done, a 250 cylinder should hold enough hot water for two showers for 18-24 hours.

Magnitio

As above, insulate all the pipes. If it is a foam insulated cylinder and there is room, add a further insulation jacket. In addition, you will need to extend the 30 minute schedule if you want hotter water as that may not be sufficient time to heat the cylinder. Try an extra 10 minutes to start with.

Coastalwatch

Hi Shibli, we have a 210 litre thermal store, well insulated as is the pipework leading to and from. Checking the data sheet it draws 81W's continuously, so circa 2kWh's per day just to maintain it's temperature even with no water drawn. As your store is 250 litres then this will draw slightly more given the same insulation. If it is being heated by an element, then probably 3kW's consumption so effectively only 1 kWh of additional energy is being injected each day! Of course if it has a different heat source then it will be another matter.

It's a shame it's in the loft as much of the heat loss goes unnoticed into the roof space whereas if it was within the living area it would make a small contribution to heating there. I appreciate space may be the over riding factor here.

Having carried out checks as per the two previous posts then I'd certainly agree with Magnito in increasing heating time from the thirty minutes currently programmed. Unfortunately, you may need to double it before arriving at a noticeable improvement.

shibli

Thank you, one other point I am on octopus go is it now worthwhile heating it by the emersion? 

michaels

How many kw is your system boiler, if it is say 20kw then in that 30 mins you are perhaps only adding 8-8.5kwh heat into the tank.

By my calcs you need a 30kwh boiler to heat 160l (two showers worth) of hot water in 30 mins.

Coastalwatch

shibli said:

Thank you, one other point I am on octopus go is it now worthwhile heating it by the emersion? 

Only if there is insufficient Solar to heat otherwise. If you regularly shower in the morning then perhaps consider heating in the last hour or so of the cheaper Go period. I notice you have an Iboost so if not home during the day then there maybe sufficient spare pv available to apply some heat during the day, well, until November arrives or our mild sunny autumn disipates. I guess the issue with heating in the afternoon is that it may gobble up a fair portion of the battery's capacity should excess solar not have been available leaving it a little drained until the next overnight Go period arrives.

shibli

michaels said:

How many kw is your system boiler, if it is say 20kw then in that 30 mins you are perhaps only adding 8-8.5kwh heat into the tank.

By my calcs you need a 30kwh boiler to heat 160l (two showers worth) of hot water in 30 mins.

The boiler is  rated as 37kw, so assume 30 mins is more then sufficient to heat 250 liters. 

shibli

Coastalwatch said:

shibli said:

Thank you, one other point I am on octopus go is it now worthwhile heating it by the emersion? 

Only if there is insufficient Solar to heat otherwise. If you regularly shower in the morning then perhaps consider heating in the last hour or so of the cheaper Go period. I notice you have an Iboost so if not home during the day then there maybe sufficient spare pv available to apply some heat during the day, well, until November arrives or our mild sunny autumn disipates. I guess the issue with heating in the afternoon is that it may gobble up a fair portion of the battery's capacity should excess solar not have been available leaving it a little drained until the next overnight Go period arrives.

I have found the iboost lacking, it was useful for some period in June/July but have now switched if off as it never really heated the water sufficiently. Its better to export the excess generation rather then attempt to heat small amount of water. I am working from home most days. 

Screwdriva

shibli said:

I have found the iboost lacking, it was useful for some period in June/July but have now switched if off as it never really heated the water sufficiently. Its better to export the excess generation rather then attempt to heat small amount of water. I am working from home most days. 

Any PV diverter would struggle with export tariffs 3-4X higher that tariffs from >12 months. Same goes for energy storage. 

QrizB

shibli said:

michaels said:

How many kw is your system boiler, if it is say 20kw then in that 30 mins you are perhaps only adding 8-8.5kwh heat into the tank.

By my calcs you need a 30kwh boiler to heat 160l (two showers worth) of hot water in 30 mins.

The boiler is  rated as 37kw, so assume 30 mins is more then sufficient to heat 250 liters. 

It's by no means certain that the primary coil (heat exchanger) within your hot water tank is able to dissipate 37kW into your tank.

See for exampke page 11 (pdf sheet 6, RHS) of this Gledhill brochure where standard indirect cylinders only have a 9 - 22kW capacity coil.