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Microwave-powered home boiler

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  • unforeseen
    unforeseen Posts: 7,382 Forumite
    Part of the Furniture 1,000 Posts Photogenic Name Dropper
    edited 17 March 2021 at 9:05AM
    glennevis said:
    I would agree with the poor efficiency. I stuck my 700W microwave oven on a smart power socket with energy monitoring and discovered it uses 1400W.
    So where is the other 700 W going?  The energy has to be used in either heating something (thermal energy) or turning the turntable (mechanical energy).
    Basing it on a magnetron's average efficiency of 65% then that alone is using just over 1kW to produce 700W of usable energy. Losses are generated in the EHT generation circuitry and the  magnetron itself.
    300-400W for fan, turntable, light and other electronics sounds about right. 
  • coffeehound
    coffeehound Posts: 5,741 Forumite
    Tenth Anniversary 1,000 Posts Photogenic Name Dropper
    One thing that would be a good use of microwave is tumble driers.  They could be used to provide the initial heat to get cold wet clothes up to 40º or whatever.  I looked it up once and apparently the Japanese were starting to use it in commercial machines.  Maybe there are safety concerns or some technical reason why they aren't used in domestic driers.
    What advantage would it have over warm air? Again it seems like an expensive way to get worse results.
    The trouble with current TDs is when attempting to initally get the laundry up to temperature.  If you imagine a pile of cold wet washing on a table and you try to dry it with a hairdryer, it would be a very slow and inefficient process.  However, once the mass is up to a decent temperature, evaporation happens more readily and the warm air process becomes more effective.  

    Microwaves are a much more effective way of banging some heat into water from cold and I would guess it would use electricity more efficiently than the warm air process despite the conversion inefficiency.  How it would compare with heatpump TDs I don't know, but it would certainly speed the process up!
  • Hexane
    Hexane Posts: 522 Forumite
    Sixth Anniversary 500 Posts Name Dropper
    If it cost the same as a microwave oven then it might be attractive to small or very-well-insulated dwellings where the cost of the heater is a significant part of the overall cost of the heating.
    I can't see there being any advantage - immersion heaters are already extremely inexpensive.
    7.25 kWp PV system (4.1kW WSW & 3.15kW ENE), Solis inverter, myenergi eddi & harvi for energy diversion to immersion heater. myenergi hub for Virtual Power Plant demand-side response trial.
  • michaels
    michaels Posts: 29,107 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    I haven't heard of these before, sounds interesting.
    The boiler uses electricity to heat water which can then be pumped through existing radiators and to taps and showers and baths. The company, Heat Wayv, is building prototypes and expects to trial the boilers in homes by the end of 2022, with the first sales to customers targeted for 2024. It says a unit suitable for a three- or four-bedroom home would cost about £3,500, the same as an equivalent gas boiler.




    Great - someone has found a way to charge £3.5k for an immersion heater in a hot water cylinder....
    I think....
  • One thing that would be a good use of microwave is tumble driers.  They could be used to provide the initial heat to get cold wet clothes up to 40º or whatever.  I looked it up once and apparently the Japanese were starting to use it in commercial machines.  Maybe there are safety concerns or some technical reason why they aren't used in domestic driers.
    What advantage would it have over warm air? Again it seems like an expensive way to get worse results.
    The trouble with current TDs is when attempting to initally get the laundry up to temperature.  If you imagine a pile of cold wet washing on a table and you try to dry it with a hairdryer, it would be a very slow and inefficient process.  However, once the mass is up to a decent temperature, evaporation happens more readily and the warm air process becomes more effective.  

    Microwaves are a much more effective way of banging some heat into water from cold and I would guess it would use electricity more efficiently than the warm air process despite the conversion inefficiency.  How it would compare with heatpump TDs I don't know, but it would certainly speed the process up!
    But they aren't more effective. It takes the same amount of energy to heat and then evaporate the water whether that's delivered by warm air or by a microwave.
  • michaels
    michaels Posts: 29,107 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    One thing that would be a good use of microwave is tumble driers.  They could be used to provide the initial heat to get cold wet clothes up to 40º or whatever.  I looked it up once and apparently the Japanese were starting to use it in commercial machines.  Maybe there are safety concerns or some technical reason why they aren't used in domestic driers.
    What advantage would it have over warm air? Again it seems like an expensive way to get worse results.
    The trouble with current TDs is when attempting to initally get the laundry up to temperature.  If you imagine a pile of cold wet washing on a table and you try to dry it with a hairdryer, it would be a very slow and inefficient process.  However, once the mass is up to a decent temperature, evaporation happens more readily and the warm air process becomes more effective.  

    Microwaves are a much more effective way of banging some heat into water from cold and I would guess it would use electricity more efficiently than the warm air process despite the conversion inefficiency.  How it would compare with heatpump TDs I don't know, but it would certainly speed the process up!
    But they aren't more effective. It takes the same amount of energy to heat and then evaporate the water whether that's delivered by warm air or by a microwave.
    Perhaps the air also needs to be circulated out of the dryer to remove the moisture thus at the start you are removing warm air before the clothes are warm enough for much evaporation to take place, heat the clothes first before applying the air and there is potentially a saving?
    I think....
  • coffeehound
    coffeehound Posts: 5,741 Forumite
    Tenth Anniversary 1,000 Posts Photogenic Name Dropper
    Billy_B_North said:
    But they aren't more effective. It takes the same amount of energy to heat and then evaporate the water whether that's delivered by warm air or by a microwave.
    I agree with the point made by michaels above.  There's almost a tug of war going on there as the evaporating water activly cools the mass, so it's a battle to get temperature into the laundry.  Microwaves give a very direct coupling of the heating energy into the water molecules.

    Since the first analogy didn't work . . how about you have a bowl of cold water.  You can heat it up using a 1400 watt microwave oven (700 watts of mw power) or a 1400 watt fan heater.  Which will heat up the water quickest?
  • coffeehound
    coffeehound Posts: 5,741 Forumite
    Tenth Anniversary 1,000 Posts Photogenic Name Dropper
    There's a few different aspects isn't there.  I suppose if you could harness all the hot air without leakage then eventually you could pursuade it to heat the laundry/bowl of water.  Speed does come into it because, to use your kettle analogy, while the 2kw kettle is heating, it is also losing heat to the environment, so it will use more energy than the 3kw.

    Also with hobs, traditional hobs slosh the heat around willy-nilly while the induction hub gives a direct coupling with the pan so uses less electricity overall.

    Heating cold, wet textiles up using hot air is a very inefficient method.  It takes so long that a good amount of that heat will be lost.  Going back to the old style vented dryers, loads of heat was ditched overboard.  I don't know how much better condenser TDs are, but they certainly heat up the room.
  • Billy_B_North said:
    But they aren't more effective. It takes the same amount of energy to heat and then evaporate the water whether that's delivered by warm air or by a microwave.
    I agree with the point made by michaels above.  There's almost a tug of war going on there as the evaporating water activly cools the mass, so it's a battle to get temperature into the laundry.  Microwaves give a very direct coupling of the heating energy into the water molecules.

    Since the first analogy didn't work . . how about you have a bowl of cold water.  You can heat it up using a 1400 watt microwave oven (700 watts of mw power) or a 1400 watt fan heater.  Which will heat up the water quickest?
    In a closed system, neither, and the tumble drier won’t be venting warm air wile it’s getting up to temperature.

    You need to remember too that the aim is to dry the clothes, not warm them, if they are losing heat to evaporation then that’s not being inefficient.
  • michaels
    michaels Posts: 29,107 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    If it is not a condensing dryer then where is the moisture going?  I can only assume it is being removed as vapour with air that is also beign released.  The warmer air is the more vapour it can hold so it would seem reasonable that the warmer the clothes are, the warmer the released air will be and the more moisture will be removed with each litre of air?
    I think....
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