Strange Gas Consumption

D_Hailsham · 7 Apr 2008

I have been monitoring my gas consumption since I moved in January 2006. As I had downsized the gas bills were lower so I did not take much notice of the actual consumption.

I have now looked at them and they seem strange, to say the least.

The system is a Y-plan with an Apollo Fanfare boiler.

The thing I find really strange is that the summer consumption (HW only) is very little different from the winter (CH and HW).

Could there be something wrong ?

Consumption:
---From ---------To---------kWH/day
21/09/2006 14/01/2007 83.49
14/01/2007 18/04/2007 97.77
18/04/2007 17/05/2007 93.29
17/05/2007 20/06/2007 86.73
20/06/2007 18/07/2007 81.27
18/07/2007 14/09/2007 71.90
14/09/2007 02/01/2008 75.65
02/01/2008 07/04/2008 81.59

ChrisR · 7 Apr 2008

Looks odd, assuming those are kW hours per day.
If your boiler is say 15kW, that means it's on 5 hours per day in the summer, which seems unlikely.

I'd be watching it, for a day!
Actually I'd set a camera up to take a picture every hour, but that's me...

D_Hailsham · 7 Apr 2008

ChrisR said:
Looks odd, assuming those are kW hours per day.
If your boiler is say 15kW, that means it's on 5 hours per day in the summer, which seems unlikely.

I'd be watching it, for a day!
Actually I'd set a camera up to take a picture every hour, but that's me...

Yes it is kW hours per day. Thanks for pointing that out; I have corrected my post.

I presume you mean photo the gas meter? Nice idea but it's an external one, accessible from the road and, in any case I have no way of connecting a timer to my digital camera.

gas4you · 7 Apr 2008

I know this sounds really stupid, but has the immersion been switched on in the winter periods? If you have one that is

D_Hailsham · 8 Apr 2008

gas4you said:
I know this sounds really stupid, but has the immersion been switched on in the winter periods?

No. The immersion is permanently off.

The HW cylinder is 140 litre with 25mm foam insulation. Unfortunately I can't see any makers name (probably hidden round the back) but it has a green label saying: "CHOICE - Energy and Environment Efficient" so I assume it is not very old. I am trying to calculate how long it should take to heat the water from, say, 15°C to 60°C. I know the equation to use, it's the kW input that stumps me. The boiler is 15kW, but obviously not all that is going through the coil, even in the summer when the CH is off. So how many kW do I assume the coil is emitting? How is this output calculated? Does it vary with temperature (like radiators, which are quoted for 75°C/65°C/20°C).

I can't find any technical details about indirect cylinders on the web.

Agile · 8 Apr 2008

Do you have a stat on the cylinder that DOES turn off the boiler when the cylinder is up to temperature?

Could the boiler be cycling because the water stat setting is never being reached?

If you dont know try turning the boiler to 80° C and the cylinder to 55° C and see what difference that makes.

Tony[/code]

big-all · 8 Apr 2008

are they all actual reading or is there any estimates there!!!

D_Hailsham · 8 Apr 2008

Agile said:
Do you have a stat on the cylinder that DOES turn off the boiler when the cylinder is up to temperature?

Could the boiler be cycling because the water stat setting is never being reached?

If you dont know try turning the boiler to 80° C and the cylinder to 55° C and see what difference that makes.

There is a stat on the cylinder wired as in the standard Y-plan which is set to 60°C. The Apollo boiler has only two temperatures Hi (80°C) and Lo (65°C). The boiler is permanently on Hi.

I have my suspicions that the boiler is undersized for the installation as, in the winter the flow temperature never exceeds 65-70°C. I was told not to worry as the house gets warm OK.

I can see this affecting the cylinder recovery time in the winter but, in the summer the flow temperature easily gets up to 80°C so there should be plenty of heat available for the Hot Water. But, as you can see from the figures, I am using up nearly as much in the summer as in the winter; so there must be something wrong.

picasso · 8 Apr 2008

well the heat has to be going somewhere, do you or your mrs have lots of showers during the summer, people staying over at weekends, teenage kids taking 4 showers a day each, and have you gas rated the boiler to see if its ok

D_Hailsham · 8 Apr 2008

big-all said:
are they all actual reading or is there any estimates there!!!

All figures are based on actual meter readings which I took. I have converted the consumption (hundreds of cu ft) to KWH using the formula shown on my gas bills.

I have found, after a bit more digging, that indirect cylinders have to comply with BS1566. Unfortunately you can only find out what the Standard says if you buy a copy and cylinder manufacturers only say that their cylinder meets BS1566.

However a bit more digging and I came across the Range Cylinders web-site. This had a table showing the following:

Reheat Performance

Indirect
Model - Reheat Time - Coil kW Rating
SI90 -- 13 Minutes --- 6.5 kW
SI120 - 17 Minutes --- 16.5 kW
SI150 - 17 Minutes --- 18.9 kW
SI180 - 21 Minutes --- 18.9 kW
SI210 - 22 Minutes --- 18.9 kW
SI250 - 28 Minutes --- 21.4 kW
SI300 - 36 Minutes --- 21.4 kW

The reheat performance is measured from 15°C to 60°C after drawing off 70% of the capacity. The coil kW rating is a guide to the minimum size of boiler required to achieve the reheat times stated.

This suggests that, in the summer, the full output of the boiler is available to heat the water. So, assuming a cylinder full of cold water at 15°C and a boiler output of 14.7kW, it will take 30 minutes to heat a 140 litre cylinder to 60°C. According to boiler mfr literature 14.7kW output requires 18.3kW input so the actual consumption would be 18.3 * 30/60 = 9.15 kWH.

But I am using up much more than this, even assuming the cylinder was completely emptied twice a day. So either the boiler is not giving out enough heat (it gets up to 80°C in the summer but not the winter) or the heat is not getting to the cylinder. How do I find out which it is?

Eeejit · 8 Apr 2008

i think Big All may be pointing in the right direction regarding
estimates. how did you work out these figures? the dates don`t all
correspond to quarterly billing. are you by any chance a master chef?
do you use gas for cooking?
recovery time for a 140 litre cylinder, not allowing for heat loss
from primary pipework and heating the metal cylinder;
net heat output 13.5 kw = 140 ( litres water)x 4.182 (s.h.) x (say)
, 50degrees -temp rise
divided by time taken in seconds
would give 2168 secs. or 36 minutes

D_Hailsham · 8 Apr 2008

picasso said:
well the heat has to be going somewhere, do you or your mrs have lots of showers during the summer, people staying over at weekends, teenage kids taking 4 showers a day each, and have you gas rated the boiler to see if its ok

Three adults in the house
Two or three showers, total, each day.
No stopovers last year.
Cold water feed to Washing machine and Dishwasher.
Gas hob and Electric oven.

Please explain gas rating boiler.

D_Hailsham · 8 Apr 2008

Eeejit said:
i think Big All may be pointing in the right direction regarding
estimates. how did you work out these figures? the dates don`t all
correspond to quarterly billing. are you by any chance a master chef?
do you use gas for cooking?
recovery time for a 140 litre cylinder, not allowing for heat loss
from primary pipework and heating the metal cylinder;
net heat output 13.5 kw = 140 ( litres water)x 4.182 (s.h.) x (say)
, 50degrees -temp rise
divided by time taken in seconds
would give 2168 secs. or 36 minutes

I answered this one in an earlier post. I won't argue about your calculations as they use the same formula as me, just slightly different assumptions.

mosaix · 8 Apr 2008

Has your next door neighbour tapped into your gas supply?

D_Hailsham · 8 Apr 2008

mosaix said:
Has your next door neighbour tapped into your gas supply?

NO

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Strange Gas Consumption

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