Instant boiling water taps

[Mark]

Instant boiling water taps...(mis)information alert!
https://www.getenergysavvy.info/post/ho ... nformation

Another of those 'must have' modern gizmos that cost the earth.....

[Catweazle]

Not a bad use of a small DIY solar or wind system though.

[PS_RalphW]

An instant boiling water tap, if genuinely instant, would need a power supply sufficient to heat water from ambient (say 15c) to 100c at the rate of flow of water from the tap. I’m not sure what a sufficient flow rate would be, so I will pick 2 litres a minute.
Heat capacity of water is 4180 joules per kilogram per kelvin. Density of water approx 1gram per ml.

Flow rate = 2000/60 = 33 ml/second. Energy needed to heat that water to boiling is 85 x 4.18 x 33 joules per second , which is about 12 KW. That is more than my shower at about 7 kw on its high setting, or about 50 amps at 240 volts, which is a lot.

A typical modern tap has a maximum flow rate of about 5 litres a minute. To boil water that fast would blow the 100 amp fuse fitted to your mains supply.

[BritDownUnder]

My company office had one here in Australia and that was not truly instant as it had a 'box' under the sink that had the water filtering, heating and chilling equipment and water tanks. I quite liked it but only drink chilled water. Whether it is any good for boiling I have no idea. My wife is a total kettle boiling nut as she drinks coffee seemingly constantly must boil the kettle at least ten times a day. I also use a lot of boiling water on the garden to kill weeds and the like but I have a 40 litre water boiling 'urn' in the shed that takes about an hour and a half to boil - quite a good use for excess solar energy. I take great pleasure pouring boiling water via a normal watering can on those pesky weeds.

[clv101]

By the time you've taken it out of the urn, filled a watering can, walked around, poured it out... is it still reliably hot enough to kill weeds?

[BritDownUnder]

By the time you've taken it out of the urn, filled a watering can, walked around, poured it out... is it still reliably hot enough to kill weeds?

I set the thermostat to 96C and when 40 litres gets to a rolling boil the whole urn is beginning to shake. I would guess you lose a degree in pouring it into the can and probably another degree heating the watering can. I take the sprinkler 'rose' off the spout of the watering can and just pour a continuous stream of water on the weed. I think it will be well over 90C when it hits the weed and supposedly you only need 55C to kill plants and seeds.

Advantages
- Can water before, during or after rain unlike roundup
- Good for sterilising plant pots without having to weed them and as long as the pot can take the temperatures. You can also plant the next seeds direct in there when it cools enough and have 'free' water.
- Good for weeds that are buried in concrete cracks as long as the cracks are not on a slope. The water has to sit there for a while around the weed to kill it.
- Good for clearing lawns prior to making raised beds - takes about 100 litres of hot water per sq metre I find.
- A good no-till method of clearing raised beds.
- No chemical residue.

Disadvantages
- Takes longer to kill weeds.
- They can come back more quickly than with roundup
- Cant kill weeds on a slope or where the water will immediately run away.
- I doubt the worms or soil bacteria like it very much.

I am looking to use a solar heating system and a MPPT diverter to do the heating soon instead of the mains.

[Catweazle]

An instant boiling water tap, if genuinely instant, would need a power supply sufficient to heat water from ambient (say 15c) to 100c at the rate of flow of water from the tap. I’m not sure what a sufficient flow rate would be, so I will pick 2 litres a minute.
Heat capacity of water is 4180 joules per kilogram per kelvin. Density of water approx 1gram per ml.

Flow rate = 2000/60 = 33 ml/second. Energy needed to heat that water to boiling is 85 x 4.18 x 33 joules per second , which is about 12 KW. That is more than my shower at about 7 kw on its high setting, or about 50 amps at 240 volts, which is a lot.

A typical modern tap has a maximum flow rate of about 5 litres a minute. To boil water that fast would blow the 100 amp fuse fitted to your mains supply.

They have a low powered heater in a well insulated pressure vessel.

[BritDownUnder]

An instant boiling water tap, if genuinely instant, would need a power supply sufficient to heat water from ambient (say 15c) to 100c at the rate of flow of water from the tap. I’m not sure what a sufficient flow rate would be, so I will pick 2 litres a minute.
Heat capacity of water is 4180 joules per kilogram per kelvin. Density of water approx 1gram per ml.

Flow rate = 2000/60 = 33 ml/second. Energy needed to heat that water to boiling is 85 x 4.18 x 33 joules per second , which is about 12 KW. That is more than my shower at about 7 kw on its high setting, or about 50 amps at 240 volts, which is a lot.

A typical modern tap has a maximum flow rate of about 5 litres a minute. To boil water that fast would blow the 100 amp fuse fitted to your mains supply.

They have a low powered heater in a well insulated pressure vessel.

The small water tank version is certainly what seems present in Australia. The power consumption was 1.3kW I think. I am pretty sure I did see an instant heated hot water tap in the toilets of a pub in the UK a long time ago.

[adam2]

Instant boiling water taps for the domestic market do indeed consist of a small pressure vessel and a relatively low powered heating element.
The heating element is 100% efficient, but losses occur 24/7 from the heated pressure vessel. Costs per litre of boiling water are very variable depending on the pattern of use.
Truly instant boiling water units DO exist but have a very substantial loading, at least 7 kw and often a lot more. More applicable to catering outlets than to domestic use.

Instant electric water heaters to produce warm water for hand washing are common. Some types are truly instant and are similar to an electric shower. they need at least 7kw to give a reasonable flow of reasonably hot water. 3 kw units exist but have a very limited flow. Very popular in warm climates were the "cold" water supply is much warmer than in the UK, BUT Not warm enough for washing etc.

Other types are in fact small storage water heaters with an insulated hot water tank of a few litres capacity. Typical loadings are 1kw, 3kw or 7kw.
The 7 kw units with a 20 litre tank will just about fill a bath with warm water.