G-save gas-saving gadget - experience?

rennysnell

This month's 'Good Housekeeping' magazine notes the following as "Innovation of the Month": "The g-save is a small device that wires into your central heating to optimise the amount of fuel the boiler uses". There's further description, and the product's website is www.gas-elec.co.uk/reduce-heating-bill.html. The cost is around £160, £220 fitted (it's not a DIY job, at least for most people).

Instinctively, I'm sceptical about such gadgets, but in this case Good Housekeeping ran their own test and reckoned they saved 31% on their gas consumption. The wesite (as above) figure quotes an average of 25%. This seems rather amazing. Can it really be so?

The device seems to work on the principle that your room thermostat does not take account of the latent heat contained in the radiator system, so turns the boiler off 'late', overheating (presumably slightly) the room; the g-save takes account of this and turns the boiler off slightly earlier than the thermostat would, relying on the latent heat to bring the room up to the set temperature - and these 'early' turn-offs add up.

Well, I can't say I'm aware of this phenomenon. I feel that, if the room(s) felt like it was cycling too hot, even slightly, I'd simply turn down the temperature setting, and presumably get the same result. Nevertheless, the GH test results look pretty good....

Does anyone have experience with this G-save device?

mech_2

rennysnell wrote: »

The wesite (as above) figure quotes an average of 25%. This seems rather amazing. Can it really be so?

Not a chance.

Gas consumption is driven by heat loss. The only way a device like this could reduce your gas bill is by reducing the average temperature of the house. The savings from a lower thermostat setting are widely held to be 10% per degree. So a 25% saving would mean something like a 2.5 degree average temperature drop for the entire time the heating is on. Since this device claims to achieve this by eliminating overshoot and overshoot is likely only to happen some of the time, the peak amount of overshoot would have to be much larger. I just can't see it being a typical case.

You should be able to get a digital thermostat that "learns" the heating response of the house and can eliminate overshoot for much less money than that device anyway.

edgex

I cant see how a system, with a thermostat, can 'overheat' the room.

In a standard domestic system there is a time lag in the heating process. The time lag is caused because the thermostat demands heat from the boiler and the boiler responds, but it takes time for the heat to get around the system, and for the thermostat to register that the water or room is now hot enough. The thermostat then stops demanding heat; but the heat that is already in the system still has to work through. In effect, because of this time-lag, the water or room is overheated.

"
How does a room thermostat work?
Room thermostats can usually be found in the living room, hallway or dining room. It controls the temperature of your whole home based on the temperature of the air circulating around the home. When the air around it is warm enough, the thermostat sends a signal to the central heating pump and boiler to stop firing and circulating water around your pipes to your radiators. Your radiators will then cool down."


So:

some lot reckon that the heat in the system still has to 'work through' (?)

yet as soon as the thermostat is triggered, to turn the boiler off, the pump will also stop, so the hot water in the boiler, & the first part of the piping, wont be pumped round the system. this heat will be lost.
there will still be heat coming from the radiators, but as this heat is given out, the thermal gradient drops, slowing the heat transfer.

so what do you do about this heat still being given off, even though the system is off?
well:
"
What times should I set my programmer to come on and off?
It really depends on you and your lifestyle. Its best to set your heating to come on about half an hour before you want your home warm, and to go off about half an hour before you go out or go to bed. "


Theoretically, you could control the boiler & pump seperately
calculate time for hot water to go from boiler & return to boiler 'T'
set boiler to turn off at 'heat off -T'
run pump until 'heat off'
also, override thermostat so boiler dosnt turn back on during period 'T'

That would give you full use of all the hot water you have produced, but theres no way that is going to be a saving of 10%+, let alone 25%!

MarkyM

I took the step at the start of 2007 of changing my hot water to come on for only 30 mins each morning and evening. Since we have a tank it gives us ample hot water we've never run out yet and my gas bills are the same they were 2yrs ago (which I guess means it's come down by circa 50% as has my direct debit payment).

Since I work from home the thermostat is always set at around 21 C, which I crank up to about 24 before the kids come home 2.30 and set back to 20/21 at about 7.30. When it's particularly mild 10C during the days I switch everything hot water & heating off.

All of our lights (even the 18 x GU10's in the wet area's) were changed to low energy at the same time. However the best thing is that all grouped electrical equipment (e.g. AV) are on those remote controlled on/off switches commonly used for christmas tree lights and I hit the off buttons are we go up to bed. Electrical usage has also stayed about the same

Since then we've adopted to small children fitted an outdoor sauna and a hot tub the latter of which is on permenantly we also run a dishwasher and washing machine daily.

Regards

Mark

CrashUK

mech wrote: »

Not a chance.

Gas consumption is driven by heat loss. The only way a device like this could reduce your gas bill is by reducing the average temperature of the house. The savings from a lower thermostat setting are widely held to be 10% per degree. So a 25% saving would mean something like a 2.5 degree average temperature drop for the entire time the heating is on. Since this device claims to achieve this by eliminating overshoot and overshoot is likely only to happen some of the time, the peak amount of overshoot would have to be much larger. I just can't see it being a typical case.

You should be able to get a digital thermostat that "learns" the heating response of the house and can eliminate overshoot for much less money than that device anyway.

I install a wireless room thermostat with timer off ebay for £50 it dont overheat as I only set at the temp I what.. this gas save thing look like a con.. I dont see how it could work with any other timer or room thermostat so I think it would cost you more money to install it.

SplanK

if the room overheats... turn the stat down a touch until its ideal... there ya go - saved you a couple hundred there with that top tip!

and i kinda agree with the pump not running thing - however you can get cheap devices which can keep the pump running for a slightly longer duration once the boiler has switched off... much cheaper than a £200 grey box!

Butsyman

I have a g-save and can report that I have seen a reduction in gas consumption over a year of about 25%. The device seems simple to me. There is usually still hot water in the radiators even when the thermostat is off and this continues to heat the room, if the g-save wasn't fitted then the system would rely completely on the room stat which are not accurate and always allow for an overshoot. Even electronic ones have this overshoot built in otherwise the boiler would have to keep switching on and off every 2 minutes to cope with temp drops up or down of just a degree. You could turn the stat down but then the room would just cycle at this lower temperature meaning that the room would have to get even colder for the stat to cut back in.

I think its an ideal device to have fitted and forget about fiddling with the stat.

ecoman_3

anything that saves me money I like, I have this gadget on my boiler and it has saved me money, therefore I like, not wanting to get bogged down by thermostat delays, latent heat (what ever that is) and such like technical babble - it has just saved me money

spiro

MarkyM wrote: »

I took the step at the start of 2007 of changing my hot water to come on for only 30 mins each morning and evening. Since we have a tank it gives us ample hot water we've never run out yet and my gas bills are the same they were 2yrs ago (which I guess means it's come down by circa 50% as has my direct debit payment).

Since I work from home the thermostat is always set at around 21 C, which I crank up to about 24 before the kids come home 2.30 and set back to 20/21 at about 7.30. When it's particularly mild 10C during the days I switch everything hot water & heating off.

All of our lights (even the 18 x GU10's in the wet area's) were changed to low energy at the same time. However the best thing is that all grouped electrical equipment (e.g. AV) are on those remote controlled on/off switches commonly used for christmas tree lights and I hit the off buttons are we go up to bed. Electrical usage has also stayed about the same

Since then we've adopted to small children fitted an outdoor sauna and a hot tub the latter of which is on permenantly we also run a dishwasher and washing machine daily.

Regards

Mark

Why on earth do you need to crank the heat up to 24c (75f) for the kids? 20/21c (68/70f) is perfectly adequate room temperature.

CEO54

I had one of the g-save devices fitted 18 months ago and can report that it has saved me 21% on my gas bill in a small 2 bed cottage, I was so pleased with the result I bought one for my parents and got it fitted by a local electrician.

I am not technical and to be honest I don't care how it works - it just does!! I saw it recommended by Good Housekeeping - that was good enough for me.

SplanK

hhmm seems to be a couple of first time posts "bigging" this up months after it got slated?!