Secondary return or trace heating tape?

Chickereeeee

I am planning to move the unvented hw cylinder to the loft. This will mean it takes longer to get a hot water flow in the kitchen. The plumber is working up a quote to include a pumped secondary return  to get instant hot water. I note there is now the alternative of using trace heating tape to heat the pipe, without needing a secondary return. This seems simpler: has anybody done this, and has any knowledge of running costs?

FreeBear

Sounds like it will cost a bomb to run at current electricity prices - Is this trace heater going to be on all the time ?

Bendy_House

Would an instant HW tap be good enough? I have to say that both your proposed solutions seem excessive for supplying a single tap.

Chickereeeee

No, it would only be on at certain times. Certainly off over night.
https://uk.rs-online.com/web/p/trace-heating-cable/2632479  suggests 9w per metre, say 10m, so 90w which doesnt sound to bad.. But real world experience?

tacpot12

You could work out the running costs if you know that rate at which heat will be lost from the pipe and the length of the pipe. The trace heating just has to replace this lost heat. e.g. if 1m of pipe loses 10 Watt per hour and the run is 8 m. You will lose 80 watts an hour, so will need the trace heating to draw 8 watts an hour. The running costs will be lower the more insulation you add around the pipe. This page should help to estimate the heat loss: Pipes - Insulated Heat Loss Diagrams (engineeringtoolbox.com)

The temperature difference it refers to is the difference between the temperature you have the hot water cylinder set to and the coldest you expect the house to get in the winter. This might be the setback/economy/night temperature you have set on any programmable thermometer. (Heat is lost more quickly if environment is colder). 

I'm inclined to think that a pumped secondary return would have cheaper running costs IF the pump is controlled by a presence sensor in the kitchen, i.e. the pump only starts running while there is someone in the kitchen, and stops when the return line in the kitchen is at a suitable temperature for water to be drawn off. The saving isn't just in the cost of running the pump but also that the heat lost from the pipe can be replaced using your boiler rather than the trace heating. If you have a gas boiler, it will be cheaper to replace the lost heat using gas than electric heating. The cost of the installation will go up if a pipe stat is required to inhibit the pump from running when the return in the kitchen is already hot enough, and a presence sensor with a timer is required to run the pump for long enough to move hot water from the cylinder to the return in the kitchen.  

Adding the secondary return pipe work is doing to be disruptive, but  so is opening the floors and wall to install enough insulation around the hot water pipe to the kitchen so that the trace heating running costs will not  become prohibitive.

macman

Any trace heat lost outside/below the loft will serve to heat the house for 6m of the year....so it's not all wasted.

grumbler

You hardly ever need a really big flow of hot water anywhere except a bath and a shower. I helped my friend to run separate 10mm pipes instead of 15mm to the sink and to the basin - and his wife was happy with the result despite being sceptical first.  This more than halves the time needed for hot water to reach the sink and the basin.

Bendy_House

grumbler said:

You hardly ever need a really big flow of hot water anywhere except a bath and a shower. I helped my friend to run separate 10mm pipes instead of 15mm to the sink and to the basin - and his wife was happy with the result despite being sceptical first.  This more than halves the time needed for hot water to reach the sink and the basin.

What a bludy great idea, Grumb! Driven by mains pressure, I doubt you'd notice any significant loss in flow.

Anyhoo, since folk are seemingly 'happy' to accept energy losses of 80W per hour or whatever, the cheapest installation solution is to attach a wee paper indicator flag to the hot kitchen handle. Set to the position that'll leave the tap constantly running at a steady drip.

No need to thank me.

Bendy_House

Chick, what use will be made of this kitchen hot flow each day? Why NOT an instant water heater/boiler for 80% of the time, coupled with an 'annoyingbutacceptable' ~30 second wait for the remaining 20% or so times?

grumbler

Bendy_House said:

grumbler said:

You hardly ever need a really big flow of hot water anywhere except a bath and a shower. I helped my friend to run separate 10mm pipes instead of 15mm to the sink and to the basin - and his wife was happy with the result despite being sceptical first.  This more than halves the time needed for hot water to reach the sink and the basin.

What a bludy great idea, Grumb! Driven by mains pressure, I doubt you'd notice any significant loss in flow.

Thank you. I'll confess then that the idea was mine too, and I  helped to implement it. 10mm plastic pipe is also very easy to work with - smaller holes, sharper bends. So not a big job really. I was tempted to try 8mm, but didn't want to experiment on the friend's house.

Chickereeeee

Bendy_House said:

Would an instant HW tap be good enough? I have to say that both your proposed solutions seem excessive for supplying a single tap.

I am also wondering that.