Gas usage sensible?

[David937]

Hello there,

I have been monitoring the usage of the heating system and I also took readings of the meter at the start and now at the end of the month.

Could you please tell me if the amount of units we have used is excessive or pretty much normal?

Beginning of month metric meter read: 6695
End of month: 7088

So that's 393 units for the cooker and the heating system.

The average flow temperature was 66 degrees and the heating usually operates 19 hours a day @ 19.5C for floor 1 and 2 and the third floors set temp is 17.5 degrees.

Thanks.

 

[Deleted member 105431]

you run the heating for 19.5 hrs a day

 

[David937]

If it was left to run automatically then it would run for 12 hours but because my mum and sometimes my sister are home all day it usually gets switched on by them.

No not 19.5 hours, 19 hours at 19.5C

 

[D_Hailsham]

Beginning of month metric meter read: 6695
End of month: 7088

So that's 393 units for the cooker and the heating system.

Are you sure it is a metric meter and 393 are the black figures, not the red?

If it is 393M³, that's about 12,500kWh in one month. My boiler only uses 26,000kWh in a year and in the last two months it has used 226M³, which is about 30% of what you have used.

You seem to have a large house - three floors. Is it an old house with poor insulation etc?

Which boiler do you have?

 

[David937]

Yes I am sure I read the black figures which read 6695 and now at the end of the month it reads 7088.

The boiler is a Vaillant ecoTEC+ 937 which is range rated at 14kw for CH.

 

[David937]

Can anyone explain why we are using so much gas?

I am trying my utmost best to make the system work efficiently;

Before the set temp was 21.5C I lowered it over the course of a few weeks to 19.5C.

I always set the flow temperature as low as possible and the average was 66C.

We always use the party mode if we go out to avoid keeping the house too warm when we are out.

I keep the doors closed nearly all the time.

 

[D_Hailsham]

Yes I am sure I read the black figures which read 6695 and now at the end of the month it reads 7088.

The boiler is a Vaillant ecoTEC+ 937 which is range rated at 14kw for CH.

Something definitely wrong then.

My boiler is a 20 year old non-condensing 15kW, so I would expect it to consume more gas than yours, but it isn't!

Reading through the history of your installation, you seem to have had many problems getting it right: incompatible controls, boiler cycling, etc etc.

You were going to install a Honeywell CM927 instead of the Vaillant control. I assume you have done this.

Presumably the CM927 and the Salus are wired to act directly on their respective zone valves. Are both zone valves wired to act as an interlock on the boiler?

I also think there may be a problem with the Honeywell and Salus not being compatible, as they work in different ways. The ON and OFF times set on the Salus are the actual times you want the heating to turn ON and OFF. During the ON times the boiler runs full blast - unless modulated down by the boiler's own control system - until the room stat turns it off .

With the CM927 the first ON time is the time you want the house to be up to temperature. The actual ON time is determined by the CM927 learning how long it takes to reach temperature and then adjusting the actual ON time. The CM927 also has optimization (unless turned off), which controls the boiler firing times when the set temperature is approached. The purpose of this is to prevent the overshoot and undershoot which is typical of many thermostats.

Your latest post has just arrived!

I always set the flow temperature as low as possible and the average was 66C.

Are you continually fiddling with the flow temperature!!?
What is the average return temperature?

 

[Tipper]

..................We always use the party mode if we go out to avoid keeping the house too warm when we are out..........

I thought party mode keeps the heating ON, because you want heat on after its normal off/set-back time if you are having a party?

Surely you should be using the 'quick veto' or 'energy saving'?
(Assuming you have a VRT 360/360f)

 

[gavinda]

i thought party was off as you have more body heat in the house. unless its one of 'those' parties

 

[Tipper]

Nudge, nudge, say no more!

In my instruction book party is defined as 'when you want the heating to continue beyond the next setback phase'.

 

[David937]

Yes I do have the Honeywell CM927 which has the optimization turned ON and as instructed by the manual I set the time I want to be warm by not the time it should be ON.

The controls seem to work very well, as soon as the temperature has been reached in any zone the boiler stops the burner and goes into pump overrun and anti cycling. The boiler remains off until any zone calls for heat, the Honeywell fires the boiler every now and again to keep the temperature steady.

When we first got the boiler I was just curious of what was going on, I am the type that enjoys watching the boiler for a pretty long time, I now find out that lower flow temperatures do no actually make the boiler cycle more.

Majority of the time the flow temperature is set at 60C/65C which gives a return of 48C when on 60C and 53C when on 65C. I lower the flow temperature down to 50C when it is anything above 7C outside.

 

[D_Hailsham]

Yes I do have the Honeywell CM927 which has the optimization turned ON and as instructed by the manual I set the time I want to be warm by not the time it should be ON.

That's good; but what is the Salus asking the boiler to do first thing in the morning?

The controls seem to work very well, as soon as the temperature has been reached in any zone the boiler stops the burner and goes into pump overrun and anti cycling. The boiler remains off until any zone calls for heat, the Honeywell fires the boiler every now and again to keep the temperature steady.

Again, that sounds good; but could the Salus be keeping the boiler running when the Honeywell wants it to cycle?

I am the type that enjoys watching the boiler for a pretty long time

TV is not much cop; and paint drying is even worse!

Majority of the time the flow temperature is set at 60C/65C which gives a return of 48C when on 60C and 53C when on 65C. I lower the flow temperature down to 50C when it is anything above 7C outside.

At a flow and return of 65/53 13kW of radiators will only produce 9.4kW; at 60/48 the output will reduce even further to 7.8kW. Assuming that, when you reduce the flow to 50C, the return drops to 38C, the output will reduce to 3.8kW. If your house is warm, this suggest that your radiators are oversized. This is a good thing as you system could then be run with a 20C differential instead of the 12C that you have at the moment.

What is the pump setting on the boiler - item d.19 on the menu?

 

[David937]

That's good; but what is the Salus asking the boiler to do first thing in the morning?

It is asking the boiler to raise the temp from 15.5C to 17.5C.

Again, that sounds good; but could the Salus be keeping the boiler running when the Honeywell wants it to cycle?

If both zones are running the Honeywell closes the 2 port valve as required.

Pump is set to automatic. Something to do with the part load, I'll check it out.

 

[D_Hailsham]

I know it's a bit late now, but what made you decide on the 937? Was it purely the hot water performance or were you advised by a heating engineer that this was needed to provide the required heating?

What was your old boiler - make and model?

The problem, I think is that your boiler is much too large for the heating requirement. The modulation range is 12-28kW and you have it turned down to 12-14kW. But your radiators are only required to provide 4-10kW, so most of the time it will not be modulating but in on/off mode.

Use Sedbuk Boiler Calculator to find out what size boiler you really need for heating. (The result includes 2kW for hot water as it is not intended for combi boilers)

 

[David937]

We got the 937 purely for the hot water performance.

The old boiler was a Baxi WM I never could find any sort of rating plate so I don't know how many KW it was, I can tell you though, that the house never really got so warm, a few rads burst when my parents moved in 19 years ago and the the thermostat never cut off the boiler because the house didn't get much above 18C.

When the boiler fires first thing in the morning regardless of the flow temp it never cycles unless of course the Honeywell CM927 tell it to.