Why do we use so much energy

GreatApe

michaels wrote: »

Compared to many on here we are energy hogs. What I am trying to figure out is whether that just reflects our usage or whether there is 'something up' with our house and or appliances.

Does anyone have any suggestions of good sites which would let us work out what our usage should be given our lifestyle?

Some frightening figures - our usage is about 230kwh per sqm per year, this excludes EV charging. GCH with a conventional condensing boiler and modern mains pressure hw tank.

Our house is a 5 bed extended semi that is supposedly EPC B (brought up from C by the PV). Our boiler is 5 years old state of the art German model with weather compensation controls. We are pretty much fully LED. WE have 5 in the house and make normal use of lighting and electronics, cooking is all electric. Heating we heat 24/7 to 21-22C in the day (6AM - 11PM) and with a night min of 17C. We are pretty keen bathers with at least 8 showers and a bath every day.

condensing boilers only operate at 'condensing mode' when heating the radiators they are less efficient when feeding hot water to your shower or taps.

You should be able to see this on your boilers pipe outside. When the central heating is on you shouldn't really see any steam (water vapor from methane combustion) come out the pipes. When hot water is run it will fire up more powerfully and you will see steam outside at least on a colder day.

The reason is the showers/taps might be pulling 15-30KW of power
While your radiators probably not much more than 2-4KW of power.
The heat exchanger in the boiler is big enough so it stays cool enough to condense the water vapor while running at the lower 2-4KW of central heating power. But when pulling 15-30KW of power the combustion has to operate at a higher temperature (at the heat exchanger) to allow the higher power to flow though the heat exchanger and at this higher temperature the water vapor does not condense so the boiler is expelling energy outside rather than using the full 90% efficiency. As a guess it drops down to conventional non condensing boiler inefficiencies when heating water so probably around the 70% mark.

Just to note I dont know any of this as a fact Im not a plumber nor have I looked into it but the above is fairly straightforward observations and strightforward physics

GreatApe

Some Ideas

You might be losing heat to the next door property especially if they dont heat their home or heat it much less than you.

Check your bathroom vents. plenty are not fitted correctly and are just a hole without shutters on the outside

Try to maximize solar gains. There are a few big trees at the end of my garden I've been planning to kill them for some time as they shade a couple of windows but I never get round to it. Also if sunny dont have the blinds closed or partially closed let the sunshine/heat in.

High ceiling properties tend to be harder to heat. As heat rises it effectively means you need a higher temperature in the property so the lower parts stay warm enough for comfort but it must mean the ceiling or upper floors are a few degrees warmer than otherwise losing heat

I am not sure what you can do to minimize this following but all the water that flows into your home during the colder months flows in at maybe 5 centigrade and gets flushed away at 20 centigrade. Might sound trivial but a family might flush the loo 50 times a day that is 300-500 liters of water heated up via the boiler from 5 centigrade to upto20 centigrade.

zeupater

GreatApe wrote: »

... The reason is the showers/taps might be pulling 15-30KW of power
While your radiators probably not much more than 2-4KW of power ...

??? .... :wall:... :whistle:

GreatApe wrote: »

... Just to note I dont know any of this as a fact Im not a plumber nor have I looked into it but the above is fairly straightforward observations and strightforward physics

:idea: ... :doh:

:rotfl:

:shhh: ... :silenced:
Z

michaels

GreatApe wrote: »

condensing boilers only operate at 'condensing mode' when heating the radiators they are less efficient when feeding hot water to your shower or taps.

You should be able to see this on your boilers pipe outside. When the central heating is on you shouldn't really see any steam (water vapor from methane combustion) come out the pipes. When hot water is run it will fire up more powerfully and you will see steam outside at least on a colder day.

The reason is the showers/taps might be pulling 15-30KW of power
While your radiators probably not much more than 2-4KW of power.
The heat exchanger in the boiler is big enough so it stays cool enough to condense the water vapor while running at the lower 2-4KW of central heating power. But when pulling 15-30KW of power the combustion has to operate at a higher temperature (at the heat exchanger) to allow the higher power to flow though the heat exchanger and at this higher temperature the water vapor does not condense so the boiler is expelling energy outside rather than using the full 90% efficiency. As a guess it drops down to conventional non condensing boiler inefficiencies when heating water so probably around the 70% mark.

Just to note I dont know any of this as a fact Im not a plumber nor have I looked into it but the above is fairly straightforward observations and strightforward physics

GreatApe wrote: »

Some Ideas

You might be losing heat to the next door property especially if they dont heat their home or heat it much less than you.

Check your bathroom vents. plenty are not fitted correctly and are just a hole without shutters on the outside

Try to maximize solar gains. There are a few big trees at the end of my garden I've been planning to kill them for some time as they shade a couple of windows but I never get round to it. Also if sunny dont have the blinds closed or partially closed let the sunshine/heat in.

High ceiling properties tend to be harder to heat. As heat rises it effectively means you need a higher temperature in the property so the lower parts stay warm enough for comfort but it must mean the ceiling or upper floors are a few degrees warmer than otherwise losing heat

I am not sure what you can do to minimize this following but all the water that flows into your home during the colder months flows in at maybe 5 centigrade and gets flushed away at 20 centigrade. Might sound trivial but a family might flush the loo 50 times a day that is 300-500 liters of water heated up via the boiler from 5 centigrade to upto20 centigrade.

I think this does all make sense. Evenn though the hot water is tank fed, each time we use hot water we are effectively using energy at x kw/h.

Presumably we should be able to do some calc using u values to work out whether the theoretical heat loss from having the house at 22/17 degrees matches the actual heat input.

I agree with you re boiler condensing range hence in one post I ask whether it is necessary to have hot water tank at 60 degrees to combat the legionella risk?

The sums on the cold water usage are presumably not to hard to dol I guess it may not all get to 20 degrees before it goes down the drain.

jennilb

In answer to the question about legionella bacteria...

Too long, didn't read:
To get legionnaires disease you need to deeply inhale quite a lot of bacteria. Provided your home is occupied and you're using water regularly, its quite hard for the bacteria to have the time to grow to large enough numbers, so I wouldn't worry about this too much.

The detail:
legionella bacteria are most able to multiply at temperatures of 20-45 degrees C. Below 20 they are dormant and temperatures above 60 kill them. However, in order to proliferate (increase to large enough numbers to pose a threat to human health) they need food and time.

I'd argue the greater legionella risk is from the cold water supply, not the hot water. If you don't have a cold water storage tank, the bacteria should never have enough time to proliferate when your home is normally occupied. If you have a tank but you're getting through the volume within 2-3 days, the risks are still likely to be small, particularly if the tank is in good condition (not full of scum / limescale for the legionella bacteria to feed on).

Run the taps for a few minutes when you get back from any period where the home has been unoccupied for a week or more, to flush out water that's been stored in the pipework and may therefore have been warmed to above 20, especially in summer, and the risk will be basically zero.

Given the home described is occupied by several people who are having showers, running washing machines, washing dishes / running the dishwasher regularly, I suggest it is safe to turn the hot water down to 50 degrees C or above without significantly increasing the risk of bacteria proliferation in the hot water system. That's because the bacteria will never have the time to multiply to dangerous levels, due to the volume of water being used.

Having the water at 50 degrees won't effect the cleanliness of hands or dishes. Hot water you put your hands in is never hot enough to have a sanitising effect, so you're relying on soap / washing up liquid for this. It would have to be at a temperature which would scald you, for the water temperature to actually be contributing to cleaning.

Most people who get legionnaires disease get it from badly maintained air conditioning units or jacuzzi / hot tubs, which produce a lot of tiny air-bourne water droplets. If you have these at home, this is where you should focus your legionella-preventing efforts.

Hope this helps

michaels

jennilb wrote: »

In answer to the question about legionella bacteria...

Too long, didn't read:
To get legionnaires disease you need to deeply inhale quite a lot of bacteria. Provided your home is occupied and you're using water regularly, its quite hard for the bacteria to have the time to grow to large enough numbers, so I wouldn't worry about this too much.

The detail:
legionella bacteria are most able to multiply at temperatures of 20-45 degrees C. Below 20 they are dormant and temperatures above 60 kill them. However, in order to proliferate (increase to large enough numbers to pose a threat to human health) they need food and time.

I'd argue the greater legionella risk is from the cold water supply, not the hot water. If you don't have a cold water storage tank, the bacteria should never have enough time to proliferate when your home is normally occupied. If you have a tank but you're getting through the volume within 2-3 days, the risks are still likely to be small, particularly if the tank is in good condition (not full of scum / limescale for the legionella bacteria to feed on).

Run the taps for a few minutes when you get back from any period where the home has been unoccupied for a week or more, to flush out water that's been stored in the pipework and may therefore have been warmed to above 20, especially in summer, and the risk will be basically zero.

Given the home described is occupied by several people who are having showers, running washing machines, washing dishes / running the dishwasher regularly, I suggest it is safe to turn the hot water down to 50 degrees C or above without significantly increasing the risk of bacteria proliferation in the hot water system. That's because the bacteria will never have the time to multiply to dangerous levels, due to the volume of water being used.

Having the water at 50 degrees won't effect the cleanliness of hands or dishes. Hot water you put your hands in is never hot enough to have a sanitising effect, so you're relying on soap / washing up liquid for this. It would have to be at a temperature which would scald you, for the water temperature to actually be contributing to cleaning.

Most people who get legionnaires disease get it from badly maintained air conditioning units or jacuzzi / hot tubs, which produce a lot of tiny air-bourne water droplets. If you have these at home, this is where you should focus your legionella-preventing efforts.

Hope this helps

Thanks jennilb