Controlling DHW to reduce gas consumption

[spluger]

craigski

the temps are set in the VRC430 weather comp thing, which is also the system brains / user interface. which is an advanced control system that modulates the boiler to be its most efficient (allegedly)

boiler temps depend on boiler type but condensing boilers only condense when the return temp is below 50'C IIRC. so the cooler you can run the boiler the better.
however the boiler circuit temp needs to be x'c above tank temp to heat it + any losses incurred  enroute

i made sure my pipes from the boiler to the 3 way valve and tank were insulated in the 25mm wall stuff. covering as much as possible right upto the boiler isolation valves


i would try setting the boiler to 60'C and the tank to 45-50'C then slowly lower boiler temp until it heats the tank in a reasonable time (remember quicker isn't allways the best)
and run the boiler once a day as mentioned and boost when needed.

what you don't want happening is the boiler running just to keep the circuit pipes hot when the tank is not calling for heat. you can test this by turning down the tank stat when the boiler is heating the DHW until it clicks off, the boiler should turn off and stay off until more heat is called for.

oh and insulate insulate insulate.


hope that helps


David

 

[craigski]

Thanks Ken/David for the pointers. I have changed the 'ON' time to 20mins (was 1 Hour) in morning, timed just before first shower and 20mins in evening. The other half has not noticed 

Checking consumption before change was 13-14kWh (not 16kWh as originally posted). Its now 11kWh, although the outside temp has been warm the past couple of days.

I will try some temp changes as recommended and post back. I dont want to change too much at same time, as I wont know what

I would love to automate this, but I think I will just end up with a summer mode and winter mode, probably with just markers on thermostats, and time changes on the programmer.

Cheers, Craig

[climber]

We have a Megaflo 210 litre and Potterton Suprima 60L boiler.

Boiler temperature set around "half way".

Timer 20 mins morning and 30 mins evening.

Gas consumption around 12kWh per day.

[dimengineer]

Thanks Ken/David for the pointers. I have changed the 'ON' time to 20mins (was 1 Hour) in morning, timed just before first shower and 20mins in evening. The other half has not noticed 

Checking consumption before change was 13-14kWh (not 16kWh as originally posted). Its now 11kWh, although the outside temp has been warm the past couple of days.

I will try some temp changes as recommended and post back. I dont want to change too much at same time, as I wont know what

I would love to automate this, but I think I will just end up with a summer mode and winter mode, probably with just markers on thermostats, and time changes on the programmer.

Cheers, Craig

Hi Craig, I think your next step has got to be shortening the lenght of your showers!! 11kWh is still an awful lot of hot water. Its around 200 - 250 litres!! ( I'm assuming in August you haven't got your heating on)

Tim

[spluger]

well so far the 45'C setting has gone un-noticed
but i'm also guessing solar input even on dull days is better than i realised


so best bet if you already have a tank get solar thermal
there's lots of different ways of connecting to existing tanks etc.

keeps us informed


David
 

[craigski]

Hi Craig, I think your next step has got to be shortening the length of your showers!! 11kWh is still an awful lot of hot water. Its around 200 - 250 litres!! ( I'm assuming in August you haven't got your heating on)

Tim

Heating is OFF.

In the name of science, here are some stats from Craig's shower this morning:

I measured flow rate whilst waiting for hot water to flow to shower head. In kitchen jug I measured 500ml in 7 secs from shower head, so that equates to approx 4 litres per minute.
Note: I do have an Oxygenics showhead fitted that reduces flow rate.

I timed my shower to be 4.5 minutes, so that's 18 litres of DHW.

I didn't time the flow whilst I was waiting for HW to run through, lets say 2 litres, so that equates to 20 litres per shower. On the basis of 2 or 3 showers per day, that's an average of say 50 litres of DHW per day for showering. The megaflo is 170 litres, maybe I'm just heating too much water?

Washing machine & dishwasher are both cold water feed.

Tim - How did you calculate the 200-250 litres from 11kWh ?

============
NOTE: I have just realised the above stats are wrong, as it doesn't take into account mixing the cold water at the shower mixer. We can assume the actual DHW in litres will be *less* than what I have quoted above.

[Iain]

Hi
Just for info, I set my cylinder temp to 45 deg C for the cut in for the boiler, cuts in if required between 0630-0700.This only tops up the heat in the top half of the cylinder so still leaves room for solar later even if only one shower is taken. (ideal for showers, but would need a higher temp boost for a bath)I have had to use a separate digital thermostat for this with a hysteresis of 0.5 deg C. The normal tank type stat has too much hysteresis (10-15 degC). I am about to change my boiler and am looking at the Remeha Avanta 18 system boiler.with an Isense controller. This will give me weather compensation, also will keep the boiler in condensing mode for the max time and also give me a built in program for temp/time for the cylinder temp It also has an anti leigionella setting that brings the water temp up once a week I think(I am not too fussed about that but others might be). Similar to the Vailant system I think.My system works very well at the moment but the boiler will need replacing soon. I have been trying to find a boiler system that does all I want in one package and I think the Remeha ticks all the boxes. I also fitted my cylinder in the loft above the bathroom so the cold run off is the minimum (about 0.5 ltr).
Iain

[brackwell]

Craigski,

I can see your still learning and understanding. In summer ( no CH ) the losses can be large and a particular one is stop/start of the boiler and all the pipes and dead ends.   Keep trying to get rid of the evening boiler use.  30 mins in the morning is my guess.

[dimengineer]

Craig,

11kWh is 11 x 3600 KJ (1kW = 1kJ/s)
 = 39600 kJ

Heat capacity of water = 4.2 kJ/kgC

Energy in = Energy out
39600 = Mass of Water x Heat Capacity x Temp Rise.
Assume temp rise is 40C (10 up to 50)

39600 = M x 4.2 x 40
M = 235 kg or litres

QED

Tim 

[craigski]

Ken - yes I'm still learning, I didn't know I took 4 1/2 minutes to shower until today

Tim - thanks for the explanation. I will loose some energy due to the boiler inefficiency that Ken mentions (I check the boiler manual, and it says 86% efficient) and the fact there is about 5m of uninsulated pipework to/from boiler and megaflo.

I need to lag some pipes next