"Instant" hot water & mid-"high" pressure system - design help needed

Thread Starter

RogueRose

Joined Oct 10, 2014
374
I'm wondering if anyone can tell me if it might be possible to make something that can heat water to near boiling and also increase pressure discharge in a workshop or kitchen sink. I'm thinking of a low flow - high pressure setup where something like 1/2 of max kitchen faucet flow is used (in my case that is probably like 1GPM at 1/2 flow) If starting temp is 120F and 190 is desired then that is ~35,000 BTU/hr which = ~ 10Kw to heat instantly which is a little out of the question IMO.

The goal of this is a compact unit that will fit under the sink.

I am thinking of using induction heating as this might be the most compact setup and the heating is pretty quick). I'm not certain what materials will work with induction heating but I know iron and copper can be heated with it so I was thinking of a copper pipe with either an iron pipe or rod running down the middle with the induction coil wrapped around the copper pipe (think of something like a condenser in chemistry).

The pressure setup is the most vexing and I'm open to ideas here. Maybe a high torque reduction gear setup (555 - 1:125) used to pump heated water into a pressurized container. This would give batch processes (which is what I'm looking for, not continuous use) and could recharge in between usage. IDK if something like a 700-1200 PSI electric pressure washer could be modified for this but those pressures are much higher than what I am looking for.

Does anyone have any ideas on how this could be done or ideas that could be implemented?
 

Sensacell

Joined Jun 19, 2012
2,449
How about this:

Gear pump to push water into tank, tank has gas or spring accumulator to control pressure / volume. This tank is very small, just big enough for heater and small volume of water. (along with requisite safety pressure relief valve)
Heating water does not warrant the complexity of induction heating, just put immersion heater in tank.

Depending on how "controllable' and 'accurate' this thing needs to be:
DC servo motor drives gear pump in response to pressure sensor or displacement of gas piston to keep tank full and under relatively constant pressure.

PID controller to control the heating of water via sensor input.
 
Last edited:

Kermit2

Joined Feb 5, 2010
4,163
+1 on the electric heating element. Induction is complex ...to make it efficient is expensive. Gas control in a residential application raises liability issues.
Look at how a keurig single cup brewer works. A few seconds wait and then 8 oz. Of near boiling water come out under med low pressure. Two such units in combo could keep an almost continuous stream of water going.
 

Marley

Joined Apr 4, 2016
283
There is no simpler way to electrically water than by having an immersed resistive heater. If you want to heat quickly, increase the power or reduce the quantity of water. The difficult bit is ensuring safety. Not only electrical safety but high-pressure superheated water is extremely dangerous. I would leave it to the experts!
 

Alec_t

Joined Sep 17, 2013
10,426
(in my case that is probably like 1GPM at 1/2 flow) If starting temp is 120F and 190 is desired then that is ~35,000 BTU/hr which = ~ 10Kw to heat instantly which is a little out of the question IMO.
Whether you heat the water by gas, immersion heater, induction, atomic power or fairy dust, due to the Laws of Physics it will still take 10kW. As stated above, an immersion heater is the simplest and most efficient.
 

crutschow

Joined Mar 14, 2008
23,481
I have used a small electrical undersink water heater, such as one of these, which plug into a standard outlet and work fine if you need only a gallon or two of hot water at a time.
If you want continuous flow then there's no avoiding more power, as others have noted.
 

wayneh

Joined Sep 9, 2010
16,114
You didn't say what pressure you want but I assume it's on the order of 150psi ± 3X. I think a small electric pressure washer arrangement would be fine - you just need a feedback loop with a pressure sensor to shut off the pump once you've hit your target pressure, with some hysteresis to turn it back on again at the low pressure set point. That's exactly how a home well pump system works. Like that kind of system, don't forget that your storage vessel will need an airspace to store pump energy. Water alone is incompressible.
 

mcgyvr

Joined Oct 15, 2009
5,394
I have used a small electrical undersink water heater, such as one of these, which plug into a standard outlet and work fine if you need only a gallon or two of hot water at a time.
If you want continuous flow then there's no avoiding more power, as others have noted.
Yes.. This IMO is one of those times where the OP should just buy something off the shelf..
Shock hazards, boiling water, high pressures, etc...

My parents had a similar device for under their sink for "instant" hot water for tea,etc... worked great.. low cost.. Held safety approvals,etc.. simple install.. still working just fine 20+ years later..

Not sure what country the OP is in but any failure of a home made device could void your home insurance claims,etc...
 

wayneh

Joined Sep 9, 2010
16,114
Yup, and they use a pressure sensor and a pump exactly as I described. I tried to fix my Keurig but the magic part is the main board, and you can't get replacements. They force you to buy a whole new one.
 

wayneh

Joined Sep 9, 2010
16,114
I've seen projects using an Arduino or such to take control of a Keurig. Seems more work than it's worth. But maybe someone has posted how to hack one.
 
Top