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Thread ID: 71115	2006-07-27 01:18:00	Hot water cyclinder:How does it work and how much power....	lance4k (4644)	PC World Chat

Post ID	Timestamp	Content	User
473877	2006-07-27 05:50:00	11.67 kWh according to me, but I am not the pedant here... My calculator gives 11.62222222. I gave only one decimal digit because, as I did say, you need to " Add a bit for the losses." The losses are significant. Perhaps I should have said "about 11 or 12 kWh". But it might be even more. Do you use inflation adjusted calories?	Graham L (2)
473878	2006-07-27 06:01:00	I converted from MegaJoules. You probably forgot the harmonic content in the mains that does not get measured accurately yet does add to the energy delivered?	godfather (25)
473879	2006-07-27 06:13:00	I used the exact conversion factors from calories to joules to kWh . ;) Perhaps you had binary "megas" . :D I don't think the harmonic component will make any difference . If it adds to the total current, the meter will register it . But the losses are going to make a bigger difference, and you will certainly pay for that . And pay . And pay .	Graham L (2)
473880	2006-07-27 06:34:00	As there are people on here with knowledge of the Hot Water cyclinder can you tell me if it is necessary to release the pressure valve on top of the cyclinder?. I was told it had to be done every six months then I was told that that is rubbish. Any comments please?.	Pato (2463)
473881	2006-07-27 06:41:00	Oh dear, Pato. There was a long thread on this subject a while ago. That is a safety device. The manufacturers say you should test it every six months. That's to give some confidence that the valve will actually operate if it is ever needed. That would be if you have a big surge in pressure in the water mains, or if the thermostat failed so the cylinder started to be a steam boiler. A bursting cylender is not a good thing. If it is full of high temperature water which flashes to steam as it escapes, it's a very nasty thing. I'd be inclined to test it.	Graham L (2)
473882	2006-07-27 06:47:00	Thanks Graham, I never saw that thread and I apologize for not doing a search. I completely forgot. Well I appreciate your comments and I wondered why it should be done and now I know. Again many thanks.	Pato (2463)
473883	2006-07-27 07:49:00	I don't think the harmonic component will make any difference. If it adds to the total current, the meter will register it. But the losses are going to make a bigger difference, and you will certainly pay for that. And pay. And pay. You assume Ferraris disk meters will measure harmonics? They do not perform at all well in that repect, sad to say. Most electronic meters will to some extent but the vast majority of metering is still Ferraris. In a holiday house just purchased this year, I noted the cylinder cupboard was a bit warm. The pipes to/from the wetback fire and the outlet were uninsulated, so I fixed that and the cupboard temperature now barely rises. Must have cost someone thousands in losses over its life to date. And no, It's not also thermosyphoning when the fire is not going...	godfather (25)
473884	2006-07-27 08:44:00	I assume that in your enquiries the objective is to 'Save Money' on the energy you buy heating your Hot Water. The smart way to save $$$$ is: - Buy a Solar Hot Water System (with storage cylinder - and you might be able to use your existing cylinder) for base load heating - designed and based on your demand (most people who supply these services will be able to help you out e.g. cylinder size, collector area size) - Back your system up with Instant Gas (lpg bottles often more economic due to lack of need to pipe from the street) for peak load demand and / or off peak sun supply (cloudy days, winter etc) - Get Quality Insulation on Hot Water Cylinder and all pipes - Get a really good installer - Most suppliers around the western world will tell you you'll save up to 75% of your energy cost on heating your hot water per year (way better than instant gas that is just cheaper than electricity) = $$$$ back in your pocket, despite the initial investment - many of these last 10 to 20+ years. - Just search google for a supplier. Good Luck S.	Stephen111 (10783)
473885	2006-07-27 18:46:00	1) The amount of power depends on the amount of hot water used (the amount of water running out the hot tap) 2) As above but if its the same cylinder, and you have only used half the heated water it will cost half as much as heating it from cold . We don't know the cylinder size, so we cannot tell you how many units it would cost to completely heat a stone cold cylinder . Again I repeat, the cost is directly proportional to the amount of water you use . There is no magic involved . The IS some voodoo involved however, Graham, and it looks like soapbox time . . . . . . . . The heating of water is not a very cost-efficient process, even under max conditions . Raising water to a certain temp from a baseline of say, room temp is always more energy wasting that is imagined . Keeping the temp at a set value (maintained) is not efficient either . I will say why a little later if you ask . Electric heating is by far the most costly in all cases; direct fire is the best and the higher the BTU's of the fuel, the better . I was always amazed that the cost per gallon of heating water rose with the temp required and the volume . Going from, say, 180F to 205F cost as much as going from 206F to 212F (boiling on the F scale) . The costs are non-linear and losses are great at the higher temps if they are not associated with pressure rise . At 1 atmosphere, the losses were greater than at 10 atmospheres . The trick is to not allow boiling . The rise in energy to get that last degree to the rolling boil is a big spike in energy use . The same with freezing water . . . . . . that last degree to change from a slurry to actual ice takes a lot of energy to achieve . This was quantified by Nicolas Léonard Sadi Carnot . The curve is still there at lower temps and pressures, just not as obvious, but wasteful in the long run . Sometimes the representation of "boiler efficiency" does not truly represent the comparison of energy input and energy output of the equipment . Remember, the initial cost of a boiler is the lowest portion of your boiler investment . Fuel costs and maintenance costs represent the largest portion of your boiler equipment investment . Not all boilers are created equal . Some basic design differences can reveal variations in expected efficiency performance levels . Evaluating these design differences can provide insight into what efficiency value and resulting operating costs you can expect . Every boiler operates under the same fundamental thermodynamic principles, therefore, a maximum theoretical efficiency can be calculated for a given boiler design . The maximum value represents the highest available efficiency of the unit . If you are evaluating a boiler where the stated efficiencies are higher than the theoretical efficiency value, watch out! The efficiency value you are utilizing may not truly represent the fuel usage of the unit . This is why steam generation for institutional heating and power is done with boilers that run at 200lbs/pressure, and 300F degrees . The losses at lower temps and pressures are too great . Needless to say, keeping the water heater at a lower temp will reduce the energy used and lower the overall cost too . It's not a linear extrapolation no matter if the container capacity is large or small . The following values are the peak of efficiency for a given boiler design, and by laws of thermodynamics are the highest achievable: Pounds Per Square Inch Degrees Absolute (psia) to temp Fahrenheit (°F) 11 - 198 14 . 7 - 212 110 - 335 340 - 429 630 - 567 1200 - 596 2000 - 636 3000 - 695 3206 . 2 - 705 . 40 The energy advocates here in the US recommend setting the temp at 145F instead of 160F for a more than 20% energy savings with just a 15F degree difference . Use of electricity to heat water is frowned upon because of the multiple energy conversions and transmissions that are required to make it ultimately heat water . Each conversion involves losses that are wastefull to say the least . OK . . . I'll pop in the reason to NOT keep the water at a set temperature: I know that most people feel that keeping the heater at the same temp is efficient . It is not . During the night when electricity usage is minimal after midnight or so, the cost of power generation goes down . Your homes and most factories shut down to minimum usage of energy, and the result is that you don't have the high spike fee values . It works like this: Energy use is computed on the peak current used by a building/home . . etc . If you turn on every appliance at the same time, you get an energy use calculation that is based upon that consumption for (in the US) the next 8 hours . This is why major users of heavy equiptment are warned to turn on the high-amp units first . This will peak the meter at a lower rate that if they turn on all the peripheral devices and then the high user . Electric motors and heaters going from cold will always draw deeply (peak demand) from the source and then they will settle down to a lower consumption . You would be wise to allow the heater to run a little hotter at night when the total amps draw for the building is lower and therefor, a lower meter rate . You'd also be banking hotter water against conversion from a lower temp later on in the morning when showers and hot water usage is higher, using less of the hotter water to acheive human requirements for a hot shower . Allowing the thermostat on the boiler to be lower during the day will help lessen the total amps used for a lower bill . See?	SurferJoe46 (51)
473886	2006-07-28 00:52:00	Joe Only about 20% of domestic houses in NZ have a time-of-use tariff, residential customers do not have a "spike" (demand) fee anywhere in NZ at present. Thermostats in most NZ houses are set to less than 75°C, as a norm (depending if the owner has had a fiddle with it). Newer cylinders are "Grade A" that have a very high intrinsic level of insulation with minimal losses, our one here has no warmth at all detectable on the outer skin. The output is tempered by a mixer in newer houses to premix with cold to deliver a lower temperature (using less of the hot water stored) for safety at the tap. The electric storage waterheaters here usually fall into two main camps, those heated on a controlled rate where the power company shed the load at their system peak times, and those that operate only on off peak (night) rates. Ripple control is used. 180, 270 and 300 litre capacites are the common sizes. Higher temperatures do result in higher losses if a poorly designed cylinder is used, but its less of a factor with a correctly designed one. Electricity as an energy source cannot be "destroyed", it can only be converted to heat, light or motive power. Losses are heat, but just not useful heat. Boiling produces steam which is vented and heats the atmosphere and agreed must be avoided in a domestic cylinder. Hot water heating accounts for 40% of all domestic load on average, where the water is heated by electricity.	godfather (25)
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