Heating on low and constant better?

Cardew

WestonDave wrote: »

However here lies the rub. Firstly we aren't measuring in tiny units of measurement. £1 is roughly 4 or 5 Kwh of electricity - that's at least 240,000 Watts difference to make even a slightly statistically significant difference in bills. By the time they've messed with the charge rates since last year as well that means you've got to see fairly massive differences to stick another £10 on a quarterly bill.

I am not quite sure what you are saying here.

Firstly 4 or 5 kWhs of electricity is more like 32p-40p for most people.

However the house in question is heated by Gas which costs approx 2.5p/kWh

What is your point about 240,000 watts? (240kW) do you mean 240kWh

WestonDave

Scientists measure in joules. We are talking in £'s. At my approximation of 25p per Kwh (nb EDF charge between 10 and 18p per Kwh including VAT for electricity not 40p), £1 = 4Kwh x1000 (no of Watt hours in a KWh) x 60 minutes x 60 seconds (I forgot the last bit - sorry!), which would give 14.4million joules per £1. That sort of measuring accuracy gives a massive margin for error within which more subtle differences would be masked as statistically insignificant. With gas at 2.5p per KWh obviously 4 Kwh per £1 becomes 40 and the whole thing scales up by a factor of 10.

If you tried to tell the difference between two 100 metre runners seperately running a time trial but could only measure the time they took in minutes you'd never see a difference. That is in effect what people are trying to do here and given the low losses in mild weather its going to be very hard to conclude definitively either way.

mech_2

albertross wrote: »

You did a whole paragraph about the construction of the house, if the house in the question is identical, then the construction is not a variable, so is completely irrelevant to the question.

Of course it's relevant. If they're well enough insulated then there's no difference between B and E for instance. If the temperature doesn't drop to 8 degrees in 8 hours the heating never comes on. Even with the heating off we don't know whether the temperature drops below the hysteresis of the thermostat because you didn't give any figures.

C is the answer whatever the construction, and that leads to the inevitable conclusion that that house will use more gas, because all other variables are identical, including the sun, the boiler, the carpets, the windows, the loft insulation, the wall insulation, the wallpaper, the kettle, the fridge, the cooker, the iron, the microwave, the human warmth, the dog, the cat, and the hamster.

No, C will lose the most heat, as per the question. It doesn't necessarily follow that it uses the most gas. You're just ignoring anyone who doesn't agree with you instead of getting to grips with the maths. Post some figures. How much would you expect to save? What would you consider an "average" house? How many houses in reality are "average"? I haven't done the maths because I tried (twice) and couldn't make it fit the observations in my house. I find it's much easier to suck it and see.

If TITEASCRAMPS gas bill is £28x12-£336 pa (assuming the DD's cover the bill), that is below the national average for a 3 bed, so if you have half of that without double glazing, then you are doing very well, or maybe you have a next door neighbour who has theirs on 24/7, and very kindly heats your house up through the party wall.

I'm going by her meter readings as DDs are never right at the end of the year. All comparisons are for October: TITEASCRAMP said 7 units a day (between 6 and 8 anyway). I used 1.6 units a day all this October at 18 deg C constant (sometimes I turned it up to 21 for 20 mins when I was feeling indulgent, but let's ignore that). If I turn my heating up to 24 in the day and 20 at night (can't sleep if it's too warm) I use 3.4 units a day as I did last year. Something's wrong somewhere. 7 units is 78KWh. If we take October temperatures as an average for the year to approximate a yearly total that would be over 28,000kWh for a year (and if I do that for my usage it underestimates by 20%, so it's a good cautious total). I was using that much with a clapped out conventional boiler that must have been under 60% efficient (judging by how much my bills went down with a new boiler).

With all due respect, if I am reading your posts correctly, the arguments are a little erratic, "Why keep burning gas when the house is warm enough?", well why heat rooms hotter than they need to be,

I don't. 18 degrees is quite low enough I think.

why heat rooms when you are out,

Because I know I'm coming back within 12 hours.

why install trv's if you aren't going to use them,

I haven't got TRVs.

why invent TRV's?

To balance the temperature between different rooms. Not to regulate the temperature of the whole house!

TRV systems usually have one or two radiators without trv's anyway (to protect the pump),

Maybe, or a bypass valve, but why let one radiator go mental when it doesn't need to? One radiator won't be able to dissipate enough of the heat to cool the return water to a low enough temperature for a condensing boiler to condense, so the heat you didn't need anyway is now being burnt at the boiler's lowest efficiency.

if all the trv's shutdown and there is no cut out/adjustment mechanism in the boiler/hall/external stat, then the boiler has no need to fire up so will use minimal gas.

Why would it cut out unless it's already kept water hot that isn't going through radiators? Hot pipes under the floor downstairs in the ventilated crawl space. Lovely. All that heat out through the flue and the airbricks.

I simplified the question for a reason, and you seem determined to overcomplicate it again with talk of fridges, building construction, and the perennial condensing boiler alchemy

So you want to ignore anything complicated to make a point you can't quantify? How does that pan out in the real world? I didn't complicate it, your theories did. I said suck it and see. How much simpler can you get?

(condensing boilers are very efficient whether in condensing mode or not, 15% efficiency gains because of condensing mode is overstating the benefits).

15% of a 500 quid gas bill is £75. If that's more than the cost of the heat lost having the heating on 24/7, it's worth pursuing if that makes the boiler condense the majority of the time instead of rarely. So how much do you save in pounds sterling in your examples?

I think sofar, we are all agreed that C loses more heat, so C wastes more heat, so C needs more energy to provide that heat, so C uses more gas to provide that energy.

False assumption. Show us the numbers.

TITEASCRAMP

mech wrote: »

I'm going by her meter readings as DDs are never right at the end of the year. .

My £28 DD is correct. After paying this for over a year the balance is £13 so it is near or damn it right.
My house temp must be near 23 deg i am always cold.

Cardew

WestonDave wrote: »

Scientists measure in joules. We are talking in £'s. At my approximation of 25p per Kwh (nb EDF charge between 10 and 18p per Kwh including VAT for electricity not 40p), £1 = 4Kwh x1000 (no of Watt hours in a KWh) x 60 minutes x 60 seconds (I forgot the last bit - sorry!), which would give 14.4million joules per £1. That sort of measuring accuracy gives a massive margin for error within which more subtle differences would be masked as statistically insignificant. With gas at 2.5p per KWh obviously 4 Kwh per £1 becomes 40 and the whole thing scales up by a factor of 10.

If you tried to tell the difference between two 100 metre runners seperately running a time trial but could only measure the time they took in minutes you'd never see a difference. That is in effect what people are trying to do here and given the low losses in mild weather its going to be very hard to conclude definitively either way.

I am a Chartered electrical engineer so I do understand units of energy and power.

I wasn’t trying to pick holes in the thrust of your argument; which I took to be that it is difficult to quantify savings/losses. I think we would all agree on that point.

I was querying why you used the price of electricity when the property in question uses gas; and anyway why use a price of “£1 = 4 or 5kWh”(1kWh costing 25p/20p!) when most of us pay around 8p for Tier 2 electricity - which is why said 4kWh or 5kWh costs 32p to 40p – I didn’t say 1 kWh costs 40p.

I also couldn’t understand the relevance of introducing 240,000 Watts(even assuming you meant Watt/hours – ) into the thread. For that matter why is 240kWh consumption relevant(cost approx £6) to this discussion.

I was puzzled not trying to be critical!

mech_2

TITEASCRAMP wrote: »

My £28 DD is correct. After paying this for over a year the balance is £13 so it is near or damn it right.
My house temp must be near 23 deg i am always cold.

Lucky you, I just had to ask for 200 quid back and I'm still in credit.

Hmm I pay 2.4p per kWh. I reckon you're using somewhere between 3 and 3.5 units a day (averaged out over the year). That's not far off what I would expect, based on my own past bills. It can't be cold enough yet to be using much over your yearly average, so the readings of 7 or 8 units don't seem to add up somehow. I wonder what happened there.

TITEASCRAMP

mech wrote: »

Lucky you, I just had to ask for 200 quid back and I'm still in credit.

Hmm I pay 2.4p per kWh. I reckon you're using somewhere between 3 and 3.5 units a day (averaged out over the year). That's not far off what I would expect, based on my own past bills. It can't be cold enough yet to be using much over your yearly average, so the readings of 7 or 8 units don't seem to add up somehow. I wonder what happened there.

Last week it was really cold, it was only 6 deg outside during the day. And really cold at night. One morning had frost on the cars
So what are you paying a year?

mech_2

albertross wrote: »

Mech,

The question I posed was about the same house, not your house, or my house, a theoretical house. The only difference between ABCDE is how you run the heating system in that house. You agreed (I think), that C would lose more heat to the atmosphere, so why bring insulation into the discussion? I've tried twice to explain that the insulation is irrelevant, because it is the same house, and either you don't get my point, or are arguing for arguments sake.

Yes we all agreed that C would probably lose most heat in a normal house, ignoring other factors etc. But the whole point from any practical perspective is the relative cost. You aren't charged by how much heat you lose, but by how much gas you burn. This doesn't relate directly to total heat loss. The total stored heat is relevant, the rate of heat loss is relevant, how the boiler reacts to different scenarios is relevant (condensing or not), other heat sources are relevant... since it's a costing exercise you even have to work out if any cost saving is worth it. If it only saves 10p a day over the winter, do I want to risk other possible consequences?

It is pointless trying to bring figures into the equation, because every house/boiler/timing/outside temp/ is different, which is why I posed the theoretical question with very few variables, to see if we could at least agree that house C would lose more heat, then move from there.

I did move on from there. To say it wasn't a good idea to draw conclusions from a theoretical question with very few variables. The question's answer is a yes/no/maybe answer that doesn't relate directly to the issue.

The question also stressed it was a conventional boiler, not condensing, to avoid the inevitable condensing mode saves 15% more arguments.

My case is rested. I give up.

I don't want to be annoying. I genuinely do want people to challenge what I say with reasoned debate rather than dismissal. A number of people said keeping their heating on made little or no difference. Some even said it showed a saving. I read the thread and got upset that peoples' experiences in specific cases were being irritably dismissed essentially on the basis of a rule-of-thumb simplification. I think that if someone's direct observations are counter-intuitive, it's better to question conventional wisdom and try and figure out why, then we might learn something.

I think that some of the official advice on energy saving is outdated. Fitting TRVs without a roomstat is a case in point. Addressed in point 4 here: http://www.nef.org.uk/actonCO2/energymyths.htm
Also I think advice formulated with conventional boilers in mind is being applied erroneously to condensing boilers when it doesn't suit them. Turning the thermostat on the boiler up to maximum in winter, for instance. That is to stop exhaust gases condensing in the flue and acid corrosion of the boiler. But you want the exhaust gases to condense with a condensing boiler!

The exceptions are always more interesting than the rules.

mech_2

TITEASCRAMP wrote: »

Last week it was really cold, it was only 6 deg outside during the day. And really cold at night. One morning had frost on the cars
So what are you paying a year?

Ah, regional weather variations! How foolish of me. It has rarely deviated from 10 to 12 degrees here for weeks.

Last year (10 Jan 06 to 13 Jan 07) I used 17758kWh of gas and paid £476.80 for it. So I paid an average of 2.68p per kWh in 2006. 4.35 units per day. That's actually more than I thought, but this is the first time I've done these particular figures as normally I do my spreadsheet for the 12 months up to the beginning of October.

This year's total will be much lower due to various things being different. So far I have burnt 6778kWh of gas since January, costing £190. My target is to not go over 10000kWh this year. Could be optimistic.

mech_2

albertross wrote: »

How much heat a house loses to the atmosphere is directly related to how much gas you need to heat it to a comfortable temperature, regardless of the boiler, the heat has to come from somewhere.

No. You're still not thinking about the issue. How many more points will you ignore which you don't like?

Fill a thermos flask with boiling water, and it will go cold. A house isn't going to outperform a vacuum flask.

A proper thermos will quite happily keep its contents at more than 24 deg C above ambient for much longer than 8 hours. Yet it has a much lower thermal mass compared to a house, no solar gain, and no internal heat sources.

If you ignore any radiative losses through the sides, all the heat loss in the thermos is in the neck stopper. Work out the ratio of surface area of the neck relative to the volume using the same units and you'll find the house wins. Ie: It's surface area is smaller per unit volume than the thermos, even though the thermos is only conducting heat through its neck. Still think the thermos wins? Depends how drafty your house is perhaps.