How does/should my HW cylinder keep warm?

[rog99]

Hello

I have a system boiler with an unvented HW cylinder.
There is a Drayton LP522 timer controller.
Separate to this, there are 2 thermostats in the house for heating control (house is split into 2 radiator zones).

My question relates to the HW cylinder.
As I understand it, water in this is kept at/around 60 degrees. When the hot taps (or mixer shower) is turned on, hot water comes from this cylinder, and is mixed with cold water from the water main feed.

The Drayton LP522 is set with 2 HW on/off times, so it tells the boiler to heat the HW cylinder in the morning and in the evening. From a pipework view, there is a feed + return between the boiler and the HW cylinder, presumably into a coil within the cylinder to act as a heat exchanger and heat the water.

Also in the HW cylinder there is an immersion heater element within the cylinder.

I *think* but not 100% sure at this point, that this is cycling on and off throughout the day, on for approx 3 minutes every hour.

This was spotted during the recent setup of some monitoring for my electric consumption, using an Owl CM180 clamp meter on the house electric feed, and a EmonCMS setup. I'm seeing 3min duration usage of 3kw - which seems too high consumption to be a fridge-freezer etc.

So, my questions are:
1) Is it likely the immersion heater is doing some of the heating?
2) Which is most cost effective - heating the HW cylinder mostly with electric, mostly with gas, or a mixture? Given the time of year the boiler isn't doing any CH duties, so would be warming up from cold each time (i.e twice a day) which seems wasteful to me.


Thanks.

 

[ianmcd]

the electric immersion heater is only there as a backup, so switch it off , there will be an isolator in the same space as the unvented cylinder, ovens and dishwashers and some washing machines also use 3KW elements, so they might be the cause of your usage spike but the immersion element should only be used as an emergency back up should your boiler fail

 

[rog99]

Thanks for the quick response. I'll give that a try and see what difference that makes.

 

[ianmcd]

just follow the cable from the immersion heater (there may be two of them ) depending on which set up you have and set the isolators to off and see how you get on

 

[stem]

Which is most cost effective - heating the HW cylinder mostly with electric, mostly with gas, or a mixture?

This is not a straight forward answer to this. As a rule of thumb, unit for unit, the cost of electricity is 3 times more than gas at point of sale. However, it will depend upon the suppliers tariffs you have signed up to. If you have an off peak (nighttime) electricity tariff, this costs less per unit, but has a higher standing charge, so unless you use a lot of electricity during the night (IE electric storage heating) it is not likely to be cost effective.

If you heat the water with gas, the boiler and pump will also consume a very small amount of electricity, but compared with using electricity for heating the water it is a tiny fraction. There will also be some minor heat losses in the pipe between the boiler and hot water cylinder, but they can be minimised further by fitting good pipe insulation.

The bottom line for most folks, unless you have electricity generated by solar, hydro or have a wind turbine on your premises, is that the cost of heating your water by gas will be less than half the price of electricity.