Navitron Renewable Energy and Sustainability Forum

General Renewable Topics => General Discussion => Topic started by: Countrypaul on May 14, 2019, 01:59:37 PM



Title: Noisy immersion heaters
Post by: Countrypaul on May 14, 2019, 01:59:37 PM
I have 3 x 3kW Immersion heaters in a 430L themal store, one near teh bottom, one slightly below mid way and one about quarter of the way down.

When any of them are in use it sounds like a boiling kettle, this is regardless of the water temperature, and being a thermal store is not due to scale build up (soft water area anyway and the TS contents are "permanent").

The TS is 600mm diameter and the imersions are all horizontal and I assume about 18-21" long.
There are no current problems with the TS other than the noise from the immersion heater(s).  The TS is located in a small under the eaves room off the guest bedroom, which until now has not been used so the noise has not been a problem.

Any ideas on how to eliminate or least least reduce the noise? I have seen special immersion heaters for sale that claim to be quieter (anyone tried them?), and also thought of reducing the voltage (and hence power) to the immersion (anyone tried this and if so how?)


Title: Re: Noisy immersion heaters
Post by: Paulh_Boats on May 14, 2019, 02:29:37 PM
Fit a solar thermal panel?

They are awesome, 30 tubes can generate over 1kW.


Title: Re: Noisy immersion heaters
Post by: oliver90owner on May 14, 2019, 02:42:12 PM
Timer switch, until the guests have got up in the morning?  A reduction in energy collection is not so much of a problem on sunny days at this time of the year?  No problem in the winter at all - unless the guests go for a nap in the middle of the day?

The problem is likely that they are high energy density immersion heaters.  Longer effective heating length is the answer, I would suggest, if the first option is unacceptable.


Title: Re: Noisy immersion heaters
Post by: Philip R on May 14, 2019, 03:39:05 PM
The power density of the heaters is too high, as oliver90 has alluded to.

When you pack in high power densities you move away nucleate boiling, as the delta T of the element to the water increases beyond a critical point, which sounds like what is going on.

Are your immersions single loop or a folded element design, i.e. a longer element folded into a shorter package.? The latter would be more desirable.

Also different sheath materials have differing surface fluid characteristics regarding boiling. I dont know which would be best. ( Our new kettle with a flat St/steel base is incredibly noisy compared to the previous element type kettle which operating at a higher surface power density.!?)

Philip R



Title: Re: Noisy immersion heaters
Post by: Westie on May 14, 2019, 05:23:21 PM
I suppose you could use a PWM controller to reduce the power to level where the heating element didn't boil?

I realise burst control rather than PWM  is preferable but could be worth a try.....

https://www.ebay.co.uk/itm/220V-ac-voltage-regulator-motor-speed-control-PWM-controller-SCR-4000W-dimmers-r/253928980064?hash=item3b1f58be60:g:XCcAAOSwGjtcbSbT





Title: Re: Noisy immersion heaters
Post by: Paulh_Boats on May 14, 2019, 05:34:48 PM
I think the term is "ebullient cooling". The element loses heat by bubbles on the surface.

The bubbles are formed when the water boils, hence it's noisy like a kettle.

Logically a longer or larger diameter element would help, which reduces the heat flux i.e heat per square centimetre. Dropping down to 2kW would also help.

Another option is AC speed controllers which are cheap on ebay, as per Westie's comment. They would adjust the power from 100% down to 0%. I have used one to reduce the noise of a powerful wood dust extractor in my workshop.

Paul


Title: Re: Noisy immersion heaters
Post by: Stig on May 15, 2019, 07:13:30 AM
The cheap and nasty way to reduce heater power is to stick a diode in series.


Title: Re: Noisy immersion heaters
Post by: Philip R on May 16, 2019, 01:04:27 AM
Stig,
the local DNO do not like customers pulling half wave DC of their supply as it can lead to uneven flux in the transformer core which in turn can lead to even harmonic currents flowing in the system. Not recomended!
Philip R