I've googled and checked the FAQ but not found anything specific to this problem.
I would like fit a decent shower in my bathroom as part of a shower/bath combination. Its a small flat with basic plumbing, 1 cold water tank and
1 hot water cylinder heated by an electric immersion heater, taps are gravity fed (except the kitchen cold mains tap).
The problem is that the shower head height is less than 10cm below the water level in the cold water tank and also heating the water is an issue.
From googling it seems I would need a negative head pump like a ST monsoon to deal with the head height. But what about heating the water? Was thinking about some sort of electricly heated shower, but im not sure what will work in this situation.
I dont have a gas supply so a combi boiler is not an option.
There nothing wrong with it, except I was kinda thinking along the lines of something that you could have an 'instant' shower with. With the immersion heater you'd have to wait till the water heated up first before having a shower.
If I was going to use the immersion for heating is there a decent brand of shower unit you would recommend that would do the job with the pump attached?
Im beginning to think I could get away with this option unless the alternative of an electric shower is not too much more expensive.
If your hot water cylinder is well insulated and your thermostat is working ok, then using an immersion heater for primary heating, would be best left on constantly, to be most cost effective.
Most of the decent brands would do this job and probably most of the cheap ones too.
As for putting in an electric shower depending on if you can get a plumber who is part P registered, or a spark who is willing to do a bit of pluming, might cost between £250 and £350 all in.
Or install a shower-coil cylinder. It has a coil at the top that high pressure mains water runs though being instantly heated by the stored water. Then a normal thermostatic shower mixer can be used.
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I've just looked up about electric combi boilers, it seems this is what I would need, assuming it pumps out hot water at a decent rate.
What kW would be needed for an acceptable shower and for running a bath? (won't be used for heating as there are electric rads here). I've seen some boilers on discountedheating.co.uk from 2kW to 12kW.
Can anyone recommend any decent plumbers in high wycombe?
The trade does appear to use the name "electric combi boiler" for what might be a suitable heating arrangement in your - unusual - situation. I came across such a thing in a holiday cottage we rented a few weeks ago
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- highly recommended! ;-) As the URL suggests, it's on Lindisfarne, aka Holy Island - off the Northumberland coast, access via causeway at low tide only. Thuz, no mains gas; property intermittently occupied by succession of short-stay visitors who can't be relied to light boilers, change gas bottles, or any such; alternatives presumably oil (but no front garden and back garden small, no access from any street!) and electric.
So they'd fitted what the mfrs literature called an "electric combi", though more accurately it'd be an "electrically heated heatbank" - there's a storage cylinder of (at a glance) 200? litre capacity, which was heated through a pair of electric elements (use one for summer, both in winter), time-controller with preference for heating during cheap-rate night-time but would boost with pricey daytime leccy if needed (OK for tenants paying multiple-hundreds for a week's stay). They'd a good programmable stat, whose default setting was more or less as a frost-stat (5 degs) with an early-morning keep-the-chill-off period; tenant override by pushing up the setpoint (with resets to 5degs programmed every 12h, to avoid using up the heat when the place was empty). HW on direct-mains (unvented) heat-exchanger off the heatbank, wasn't interested enough to work out whether the CH feed came off a heat-exchanger or circulated the stored water - but in either case the CH was very responsive.
With only two bedrooms and a bathroom upstairs, and a largish open-plan living area downstairs, this arrangement was perfectly adequate to keep the place toasty-warm on its own - though we dig bring up three office-moving crates full of wood for the multifuel stove for the prettiness off it, and in case of powercuts. The tenant instructions asked us not to fiddle with any of the controls, and so I avoided the temptation to switch to the 'winter' position (both heating elements). I believ therefore that the heating (and the bath filling) was done with a single 6kW element; if one was living there permanently, with more of an eye on the running costs, I think you'd want to make use of the 'winter' position to get both elements going in winter, purely to get the bulk of the energy consumption done on cheaprate. The place was reasonably insulated - gert thick walls, well-fitting windows - and being terraced had only the front and rear exposed; but exposed to seriously chilling winds - this being an island in the North Sea, after all!
Hope the thumbnail above suggests hope, in that case - 2kW sounds stupidly small, 12kW may be overkill (but would give you relatively fast recovery, at the cost of needing a hefty feed (50A circuit, may need to get yor supplier to uprate their incoming fuse).
Rocking-horse droppings come to mind ;-)
Ob. thread-drift (but still d-i-y): we drove onto Lindisfarne on a Saturday, parked the car, and didn't try to move it till the Friday. Started just fine, but wouldn't move - felt as if it'd been clamped; well, it *would* move, but only by dragging the non-rotating rear driver's-side wheel over the gravel! Turned out the saltwater spray + damncold winds (this was February) had made the handbrake shoe seize up (big clue: handbrake handle inside the car wouldn't come back up once released). While waiting for the RAC to show up (hey, it's paid for, may as well use it) tried - on the suggestion from the man in the Local Shoppe ;-) - tapping it free with a suitable hammer substitute (wheel wrench, since you asked - I'd jacked up that wheel and taken it off, for better access and trying to work out Wot Wus Going On. A couple of non-vicious taps, a satisfying 'ping' of releasing spring, and the wheel turned freely! Result! RAC callout cancelled, off to Berwick...
Thanks for the info there Stefek. After some consideration I think going for one of these "electric combi boilers" is not really what I need. A gas jobbie would be perfect, unfortunately no gas here. So what someone else suggested on uk.rec.motorcycles was to use a mains electric shower. They are cheap and should be simple enough to install without the hassle and expense of ripping out the old tank etc..
Thanks for the tip about the handbrake on the car by the way, never realised that could happen!
They're certainly straightforward to install. (Don't, though, make the allegedly common balls-up of trying to run them off an existing socket circuit! They need their own, dedicated circuit, most often run in
10mmsq cable with a 40A breaker.) I find them fine for showering under, but plenty of others prefer much more of a downpour for their shower.
An instantaneous heater just can't produce the hefty flow which some people like (basic physics intervenes: water just takes a lot of energy to heat up!). So, with a 9kW electric-instant, you're not going to get more than a 'few' (can't be bothered doing the calculations yet again!) litres/min; with a combi which goes up to say 24kW you'll get more - about enough for most people's idea of a decent shower, but still relatively slow to fill a bath and a PITA if other people are using hot water at the same time. The effect is more pronounced in winter - to get from incoming temp of say 5 degs up to comfortable showering temp of about 40 is nearly twice the stretch than from a summer pipe-temp of
15-20 degrees. Hence the use of some sort of storage arrangement, so the heating can happen over a longer time than the usage - whether that's a conventional hw tank, heatbank, or the built-in small storage which some combis have to give a higher initial flowrate...
Nor did I, but I do now. Apparently it's common practice Oop Their Way to leave the car in gear but handbrake off - though the island's not quite pancake-flat, the bits with the roads all are...
So here's the amazingly detailed back-of-an-envelope calc. Takes
4.2kJoules to raise 1 litre through 1 degree C. A reasonable midpoint for how much temp rise you want is 30 degrees - from 10 to 40; so handwave it to 120kJ for each litre. A nice round number, that, since we want our final answer in litres/minute - since 1kW means 1kJ/sec, to get
120kJ in a minute we want 2kW.
Thus, rule-of-thumb-close-enuff-for-jazz says 'shower delivery rate, in litres/min, = half of kW rating'.
Sanity-check: that says a 9kW leccy shower puts out 5L/min. That's rather below the mfrs advertised figures - e.g. Goolgle says dealtime.co.uk describe several 10.5kW showers asdelivering "up to"
14L/min. Either there's a mistake in basic physics... or, the "up to" figure is for a lukewarm shower (30mumble) in summer (incoming at
20mumble, at least until the prewarmed water in the house cold water pipes has all come through and you drop back to the underground temp closer to the low teens). Second sanity-check: 1min for a litre through
30degs with 2kW input says a 2kW kettle will take 3 mins to boil (90 degs rise needed) - yup, that's consistent with normal experience. Third sanity-check: combi specs at the top of my Google results for 'combi "litres per minute"' say '28kW 11.4 lpm' and '27kW 11 lpm', for a
35degree rise; perfeckly in line with the rule-o-thumb derivulated above.
So that's two-out-of-three sanity checks in line with Normal Fizziks, and one out in creative-marketing-specmanship land. Pretty normal, then ;-)
As the final answer to this sort of calculation is usually needed in kW or kWh I find it useful to remember the heat capacity of water as 1.16 Wh per litre per degree. 1.2 Wh is near enough for most purposes.
Cool (or, more exactly, warm ;-) For litres/min we transform 1.2Wh to
72, well, 70 Wmins; which tells us that for a 30 degree rise we need
70x30 = 2.1kWmins, agreeing with the previous sketch.
The best aide-memoire I've come across (and therafter remembered!) for such "cached" intermediate results is "pi seconds is a nanocentury" - i.e. in a year there's 3.gubbins x 10e7 seconds. Useful when you're roughing out 'X things/sec, how many X in a year?' or similar.
Then there was Grace Hopper's visual-aid-memoire: in some of her talks she handed out 'nanoseconds' - one-foot lengths of wire, for such is a (useful approximation to) the speed of light/electrical-signal propagation - the relatively small (10-20%) differences between speed of light in a vacuum, and electrical signal in copper, don't matter much for these rule-o-thumb mnemonix; and it's kinda instructive to realise that as memory buses in ordinary PCs approach GHz speeds, the distance on the motherboard from CPU to RAM is 'significant' - half a cycle or more...
For pi itself everybody knows 22/7, but far fewer can recall 355/113 - remember it as 11-33-55, split in the middle with the first half as denominator - and that gets you within 0.1 ppm or 6 decimal places of the real true pie.
Funny, before I even got as far as that paragraph I was thinking "one foot per nanosecond"...
For something slightly more on-topic, how about 60 bricks per square metre (for half-brick thick stretcher bond)? Or ten ft^2 in a m^2 - that's about 7% out but still useful for rough estimating or heat loss calculations.
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