I've been pursuing the cost of DHW. I was working off a report by the Energy Saving Trust
formatting link
of 2008, which indicates that their survey identified a statistical mean household consumption of ~120 litres/ day which I haven't done the full sums on, but from their figures I'm getting 5kW energy. One thing that I did find interesting is that this average is 116 L for a tank system and 142 L for a combi; there is no explanation of this which I'm sure is obvious to others.
I went off to follow the topic further and found that the Engineering Toolbox website gives 90 to 160 litres / day / occupant for a house for hot water consumption.
This is such a massive difference that I wonder who is right?
Splutter! How big a household? I think it would take me a month to get through that, so what sort of horrendous consumption is on the other side of the mean?
That sounds about right. Various documents say that flushing uses half your water consumption, since I put in a rainwater harvester for the loo the water meter claims I use about 40-60 litres per day. That includes a full load washing machine every two weeks, and a leisurely shower a varying numebr of times a week.
All these numbers are averages and may not be right for you in any case. You need to sit down and think about how many baths/showers you take/ day etc. The other aspect is the heat loss from the tank which depends on the insulation. New tanks have this marked on the label. Remember this is the heat loss from the time when the tank is at working temperature.
Another factor is how far the tank is from usage points. This is the one that is responsible for the increased water use in the combi. However the heat loss for a combi is reduced as there is no water stored.
Thanks. Variables that I might be considered significant - such as household size - seem to have a very low positive correlation with increased HW consumption. Dishwasher would be one of the most interesting, but hasn't been included even though 'kitchen sink' has one the highest flow rates. (money cost by energy type not considered, though). There;s something slightly unhinged about that report that I can't see just yet.
They put it down to flow I think - combis they say are higher. I can't see the explanation in the report, but it may be something like the initial warm-up - longer with a combi. The graphs on p.27 are difficult to follow - which tends to suggest there's a human factor at play - such as more likely to top up a combi boilered bath. Don't know!
Small sample of the report, and it's one of those things that varies massively by household. Shower and dishwasher household might use less than half that of a bath-sink household.
I can tell you that I use around 3-4kWhr/day for one person on hot water, which includes a shower. It increases by 1kWhr in the winter, presumably due to the water starting off colder, but it might be due to higher consumption too (more likely to wash hands in hot water, perhaps). When there's more than one person, the figures are very inconsistent.
This is gas consumption, using an indirect hot water cylinder.
When i had my motorhome, touring europe for a few months, i averaged one fill up of water every 6 to 7 days, that was 140 litres of cold water,
20 litres was stored in the calorifier (small hot water cylinder, heated by the engine's coolant when driving, the eberspacher 5kw heating boiler or a
1kw mains element)
Ok the flush bog was a button operated solenoid valve, so you only flushed as long as needed to clean the bowl.. handy when the bog's waste tank only held 20 litres (would empty that 3 or 4 days, depending on my gut condition )
Showers were taken as needed... 3 or 4 a week each, but it was 'water on... get wet, water off, soap up and lather, water on, rinse off, water off' etc, rather than leavin the shower running for 8 minutes like at home.
When i fitted a washing machine (candy aqua 1000T... 3.5 kilo load front loader) the water consumption figures were screwed up, the washer took 38 litres for a full wash cycle, so i'd ensure there was about 50 litres in the tanks, then drive to the next stopping place with the washer running, then re-fill the tanks when i got where i was going, and dump the waste tank too.
It is amazing how living with tanked supplies for a while trains you to be economical, you think about how much water your going to use and reduce it if you can... especially when your running low, likewise you think about what you dump down the drains as you have to move the vehicle to a dump point when the grey tank is full, when i had gas heating that was a pain, especially not having a gauge inside the vehicle, so every few days i had to check the tank gauge, found out i could last 12 days on 27 litres of lpg running the water and space heating, and then had to drive to a refill station,
i then changed over to diesel centeral and water heating, and 50 litres of red diesel would last 25 days in winter, as i never stayed more than 2 weeks in one place that was easy to plan a re-fill, plus i could always siphon some road diesel out of the vehicle tanks if i really needed to (providing i wasnt running on bio diesel at the time... as the 12 volt eberspachers dont like bio, 24 volt ones do tho!!)
Or i could take a jerry can to a petrol station, tho apparantly you 'can' re-fill a lpg tank from a lpg bottle with an adaptor and turning the bottle upside down after opening both valves.
Mind, when i changed girlfriends, the new one had to be trained to be economical with power and water, she'd leave taps running when cleaning teeth, pausing to pick her nose and do her hair with the toothbrush in her mouth... took a few times of me letting her run the tank dry before she learnt, and now she has a go at me at home for wasting water.
Thanks Andrew - it's interesting that using some ballpark figures I reckoned on 5kW requirement per day. That's with 2 of us in the house.
This all came about from a Solar Panel salesman suggesting a thing called the Immersun which directs the 'off peak' output to the tank immersion heater. I was trying to estimate the payback time.
Yes, of course, but that saves on 'hot water flow rate' - the measure in the report.
Indeed. But our combi takes over a minute to get anything approaching hot water to the bathroom basin 4 storeys up. This all adds to the 'hot water flow' - even if it isn't hot at the receiving end.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.