New Smart Instant On Water Heater - Page 1
Forum section: electronics / general

author: SgtRock
author_rank: Unknown
timestamp: April 10, 2012, 10:48:37 am
content: Greetings EEVBees:--See the below link to learn about a new water heater design, that may have merit. I think if it performs as described, it will see wide use. And remember, if it were a completely useless, hopeless technology, the US would loan it a billion dollars or more.http://www.postandcourier.com/article/20120409/UNKNOWN/120409228/1165"Get ready, little lady. Hell is coming to breakfast."Chief Dan George 1899 1981Best RegardsClear Ether

author: Write_to_Smokegenerator
author_rank: Regular Contributor
timestamp: April 10, 2012, 11:23:34 am
content: Lets see how good this will work.Would love to use less energy for water heating.cheers.

author: SoftwareSamurai
author_rank: Regular Contributor
timestamp: April 10, 2012, 11:36:24 am
content: I wonder what happens when you put in pure H2O, which doesn't conduct electricity?

author: rsjsouza
author_rank: Super Contributor
timestamp: April 10, 2012, 12:21:43 pm
content: It is popular in Brazil an "instant heater" that is a shower head with a built-in massive (2~8kW) resistance that heats the water instantaneously. Based on the same principle there are electric faucets as well.Example:http://www.cardal.com.br/du_suprema.html(portuguese only, sorry)Internal diagram:http://www.newtoncbraga.com.br/index.php?option=com_content&view=article&id=2936:el033&catid=115:instalacoes-eletricas&Itemid=101(portuguese only, sorry)Although the wiring had to be somewhat critical, since it requires a solid path to ground and enough cross section to drive such large continuous current (not rarely I saw 6 or even 10mm wire on the more distant circuits), the fact it does not have to spend energy to maintain water heated all the time makes it for a lower electric bill at the end of the month - I used both systems and I can attest that.Obviously that each water outlet requires a heater, therefore the upfront cost may not be very attractive for the colder climates...Another detail that drives some people off is the quality of certain brands... Which would make a nice instantaneous body toaster...

author: saturation
author_rank: Super Contributor
timestamp: April 10, 2012, 12:29:11 pm
content: Its basically a tankless water heater, the idea has been around for >40 years.http://en.wikipedia.org/wiki/Tankless_water_heater#Tankless_heaters

author: T4P
author_rank: Super Contributor
timestamp: April 10, 2012, 12:29:47 pm
content: We use them all the time due to the space savings and that we aren't all living in big houses due to the mad housing prices .I don't know what's the rating of them oh well , but they have massive elements that get the temperature set there in the ranges of milliseconds but always miss by about 5C , then settle down quickly .They regulate damn well .

author: G7PSK
author_rank: Super Contributor
timestamp: April 10, 2012, 09:15:59 pm
content: We have had electric showers for years here. This is an example from the many on the market.http://www.discountedheating.co.uk/shop/acatalog/Mira_Escape_9.8kW_Thermostatic_Electric_Shower_-_Satin_Chrome.html

author: IanB
author_rank: Super Contributor
timestamp: April 10, 2012, 09:48:22 pm
content: A slight snag is that heating enough water for a shower at a decent flow rate requires a lot of power. The UK market is flooded with instant electric showers at powers up to 10.5 kW. These require a 50 A breaker and very thick wires in the shower circuit (10 mm2 or 7 AWG). Even at this extreme power rating the water flow is only just enough to provide a decent showering experience.

author: T4P
author_rank: Super Contributor
timestamp: April 10, 2012, 11:47:53 pm
content: Quote from: IanB on April 10, 2012, 09:48:22 pmAKA water flow that comes out unboosted .

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2012, 12:02:15 am
content: Quote from: Dave.S on April 10, 2012, 11:47:53 pmDid you think for even a second before you wrote that comment?

author: T4P
author_rank: Super Contributor
timestamp: April 11, 2012, 12:34:17 am
content: I did , mine doesn't have a pump , at least . Neither do most of them .

author: vk6zgo
author_rank: Super Contributor
timestamp: April 11, 2012, 12:54:55 am
content: The whole idea of having contact between the water & the mains freaks me out.I don't trust a "microprocessor" to save me from being zapped.But maybe it is transformer isolated.Instant electric HW heaters were "all the go" in Oz back in the late '50s,but they used heating elements close to the shower head in the "most instant"case,or otherwise,a box on the wall!They lost favour,in Western Australia,at least,due to the safety angle,& lack of reliability.Most people ditched them for solid fuel,gas,or in an increasing number of cases,Solar,which offered a full HWS for the whole house.I don't think,despite the report's wild enthusiasm,that there is a mass market out there.--Maybe for cheap flats (apartments),or holiday homes.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 11, 2012, 01:35:17 am
content: There are water heaters that use heat pumps. They're a lot more efficient (2-3x as efficient) than the normal ones, but obviously cost a lot more as well. They also have the side benefit of cooling down/dehumidifying the space they're in.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2012, 02:18:38 am
content: Quote from: vk6zgo on April 11, 2012, 12:54:55 amThey still are very common and popular in Britain:http://www.showerdoc.com/showers/electric-showersLook how many there are! I think the popularity may be because getting a good shower in Britain is otherwise very difficult. Standard hot water systems use gravity feed from the loft and there is not enough pressure to run a shower in an upstairs bathroom without installing a booster pump.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2012, 02:23:52 am
content: Quote from: Dave.S on April 11, 2012, 12:34:17 amRight, but that has got nothing to do with the power demand of instant water heating. Go back and read my post again. Then read it again. Then think about it. Then think about it some more. Then stop posting crap without thinking. In fact, don't post crap even if you think about it first. Just stop posting crap all over the forum.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2012, 02:41:39 am
content: Quote from: vk6zgo on April 11, 2012, 12:54:55 amSince all electric heaters are by definition 100% efficient, inventing a more efficient electric heater is a mug's game. The only economic and engineering justification for coming up with a different design is that it is simpler, or cheaper to manufacture, or more reliable, or performs better, or some other advantage. The only advantage I can infer from this particular design is better and faster temperature control, which is sometimes a shortcoming of conventional electric showers.Unfortunately, laws of physics are against you. Here are the power economics of instant electric showers:Firstly, the minimum water flow for a pleasant shower is about 6 l/min (1.5 US gal/min). This is still quite low and 10 l/min is much more pleasant. However, let's go with 6 l/min. That works out at 0.1 kg/sec.Next, let's suppose the water supply is at 15°C and we want to heat it to 45°C, which is about the temperature of a pleasant warm shower. That gives a temperature rise of 30°C. Given an approximate specific heat capacity for water of 4200 J/kg-°C we can work out the power demand as:W = (flow) x (specific heat capacity) x (temperature rise) = 0.1 kg/sec x 4200 J/kg-°C x 30°C = 12 600 J/sec = 12.6 kWGiven a 240 V domestic supply, we will need 52.5 A to deliver that power. That's really stretching a typical domestic power circuit. In fact, most showers in the UK are between 7.5 kW and 10.5 kW. You can tell that they will only provide a piddling flow of water if you want your shower water to be more than tepid.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 11, 2012, 03:59:35 am
content: Quote from: IanB on April 11, 2012, 02:41:39 amResistive heating can only be 100% efficient, but it's possible to get more heat with the same electricity input by using it to move heat from another source. Heat pumps can be 2 or 3 times as efficient as resistive heaters at the temperatures you're dealing with. It won't solve the problem for that particular use since a heat pump that big would be very expensive, but it's theoretically possible.There's another trick that also greatly reduces the energy needed. Since pretty much all of the heat goes down the drain, use a heat exchanger to recover a good amount of it.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 11, 2012, 06:00:02 am
content: Quote from: IanB on April 11, 2012, 02:41:39 amI forgot to mention earlier,that 3 phase instant water heaters were not uncommon in WA,either,but they were a HWS for the entire house.With less current per phase,they could probably make it to 12.6kW.They certainly gave ample hot water when they were working.The problem with them was complexity,they had water pressure operated switches which would eventually drop a phase,& the whole thing would need to be pulled out for replacement.Ours blew a phase, back in 1988,so we dumped it & got a Solar HWS.

author: amyk
author_rank: Super Contributor
timestamp: April 11, 2012, 07:28:35 am
content: Quote from: rsjsouza on April 10, 2012, 12:21:43 pmOr how they're installed...http://thereifixedit.failblog.org/2009/11/24/i-can-never-remember-if-i-wiggle-the-red-or-green-wire-for-hot-water/http://thereifixedit.failblog.org/2011/08/03/white-trash-repairs-thank-god-for-that-sign/

author: Rerouter
author_rank: Super Contributor
timestamp: April 11, 2012, 08:28:20 am
content: the main thing i would be pondering with current passing between electrodes in an electrolyte would be corrosion over time, be it one plate to another, or the pipe to the electrodes...also... it seems it would be dumping current into most houses earthing system.. which i see as a problem, unless its isolated somehow, but still seems difficult then as there would be 2 electrodes, so 1 would pass some current to earth relative to the other...

author: G7PSK
author_rank: Super Contributor
timestamp: April 11, 2012, 10:44:16 am
content: If the current to heat the water flows between the shower head and a metal shower tray/bath you will never have a dis-satisfied user or complaints of low pressure or temperature or any warranty returns either.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: April 11, 2012, 10:57:03 am
content: Quote from: NiHaoMike on April 11, 2012, 03:59:35 amI have aways wondered why electric showers aren't made like that ,with a simple heat exchanger something like a simple two walled copper tube with the warm outflow water pre-warming the inlet .Even if we only catch 50% of the heat from the outflow that 50% less power needed for a given flow rate . Seems like a no brainer ,I must be missing something I guess ,there must be some sorta reason they arent made like this .?

author: cybergibbons
author_rank: Frequent Contributor
timestamp: April 11, 2012, 12:05:22 pm
content: Quote from: kevotronic on April 11, 2012, 10:57:03 amLoads of reasons:1. Pretty hard to recover heat from 38°C water into 15°C water efficiently in the best circumstances.2. The water probably cools a lot between the head and the drain, so you might be trying to recover 25°C into 15°C water.3. The outflow from the drain must be free flowing to comply with regulations. Hard to make an efficient heat exchanger that has a mixed flow of liquid and air.4. The outflow will contain soap and other containments, which will quickly dirty the heat exchange surface.5. Makes plumbing much more complex.6. Probably going to be a long time before you recover costs.I can see value in collecting all warm waste water from a house and then using a heat pump to recover energy - this has been trialled. But a simple heat exchanger at point of use doesn't seem like a good solution.

author: T4P
author_rank: Super Contributor
timestamp: April 11, 2012, 05:06:32 pm
content: Quote from: IanB on April 11, 2012, 02:23:52 amWell , that has got to do .With a pump you have to deal with needing a lot more heating power .

author: SeanB
author_rank: Super Contributor
timestamp: April 11, 2012, 07:50:25 pm
content: Nothing wrong with a standard stored heat geyser. I added extra insulation ( did some drywall work and had a few metres of Isotherm left over) so it now is a green ball. Insulated the piping going in and out ( that will drop the power use by half in standby if you only insulate the first meter of pipe using Armaflex) till they went into the shower and the ground respectively. Now only problem is that the cold water has a distinct warm slug if I use the basin, just from conducted heat in 5m of piping. Extra insulation does pay for itself.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 14, 2012, 11:16:37 am
content: @amyk, loved these pictures! I've seen my share of crazy installations and I wish I had a camera then...

author: Zero999
author_rank: Super Contributor
timestamp: April 14, 2012, 02:52:42 pm
content: Quote from: Rerouter on April 11, 2012, 08:28:20 amIt's an electrode heater which also been around for years. The only novel thing seems to be it's being used for instant heating.Corrosion isn't much of a problem with AC because the current changes direction before the ions have time to migrate through the solution.You're right about some current going through the earth but it'/s not that bad because the neutral is positioned to minimise earth leakage. There are special wiring requirements for electrode water heaters in the UK. I don't know about the US. I'd imagine that using an isolation transformer would eliminate the earth leakage and special wiring requirements.

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2012, 03:10:19 pm
content: With the cost of an isolating transformer for 5kVA plus i would buy a heating element and geyser every year and still come out ahead. In most cases electrode boilers are designed to have a good earth connection, as there will be current flow there. The most common use I have seen is a 3 phase unit used to make steam for use in a plant, where it uses a 380V 3 phase supply, at around 60A per phase, so as to generate a very fast reacting steam supply that is much smaller than a standard oil or coal burner, and without needing a large oil tank or coal bunker. They are meant for permanent installation, with a earth current monitor that will trip at the amp level, for phase faults.For a domestic instant water heater it is more likely that it uses a high density heating element, with a spiral wound element exposed to the water flow. A short life for the element because of temperature cycling, and the actual resistance wire runs at probably close to white hot to get the heat flow across the MgO insulation high enough to heat water fast. The only domestic electrode boilers I have seen are clothes steamers, which need a salt dose to run, and which are double insulated, with water filling being done only when disconnected from the mains.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 14, 2012, 03:24:08 pm
content: Might it be possible (probably not practical for general use) to use a high frequency AC output switching power supply to provide the isolation? With a high enough frequency, it might even be possible to capacitively couple through the glass or whatever. Seems like something that could be useful for heating corrosive liquids.

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2012, 03:38:41 pm
content: You can buy that off the shelf, in a box labelled "Microwave oven". At lower frequency you use a big one to heat metal for recycling. If you build it big enough you use plain mains as the frequency source, and it uses megawatt power levels for smelting steel.

author: Zero999
author_rank: Super Contributor
timestamp: April 14, 2012, 05:39:31 pm
content: Quote from: SeanB on April 14, 2012, 03:10:19 pmAn electronic transformer, similar to the sort used for halogen lighting, would be much cheaper. The output waveform doesn't need to be pretty, all it needs to do is put a high enough voltage though the water to heat it to the desired temperature.It has a microcontroller anyway so I wouldn't be surprised if it controls a pair of IGBTs/MOSFETs connected to a high frequency transformer, forming a SMPS similar to that of an induction hob.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 15, 2012, 11:17:34 pm
content: Found a good one at my mother in law's home.Fortunately this bathroom is being used as a deposit, and not for showering...In any case, I asked her to remove everything in case anyone has any "brilliant ideas"...