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gchiu

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#260052 8-Nov-2019 12:22
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Looks like the biggest obstacle to going off grid is the amount of energy used for space heating.

 

So, what about low flow temperature water radiators?  Most radiators need to run at high temperature but these beasts use the same temperature as hydronic systems while preserving the footprint of a traditional radiator

 

https://www.mesh-energy.com/low-flow-temperature-radiators-the-next-best-thing/

 

 

 

 

There are a couple of mainstream radiators on the market that fit the bill and allow underfloor flow temperatures to heat a room whilst retaining the same ‘wall print’ size as a traditional radiator. Low flow temperature radiator designs take advantage of compact but highly efficient multiple small bore pipe and a lightweight aluminium fin design to maximise the area emitting heat as well as the option for convection fans to boost output.

 

 

 

 

I see that there's a supplier of such systems in Naenae so will go to have a look.  But potentially maybe one could hook this up to thermodynamic panels and end up with very low cost space heating?


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elbrownos
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  #2350245 8-Nov-2019 14:29
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Where's your heat coming from?


gchiu

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  #2350256 8-Nov-2019 14:45
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I'm suggesting thermodynamic panels which produce a water temperature of 55 deg C.  This isn't hot enough for standard radiators but would suit these low surface temperature ones.


 
 
 
 


gchiu

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  #2350744 9-Nov-2019 14:10
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Having more information from the distributor a 1.6 kW heater uses about 18 1W fans to push air across the radiator.

 

So, 18Wh of electricity to move 1.6kWh of heat into the room.  

 

The 1.6 kW panel looks like the largest they sell at 2000x900 mm in size


mattwnz
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  #2350746 9-Nov-2019 14:19
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Think one of the manufacturers had a display at the home ideas centre. The other company is leap. All in lower hutt. 


gchiu

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  #2350756 9-Nov-2019 15:42
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Had a look at the Home Ideas website ... no display there now.


SomeoneSomewhere
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  #2350862 9-Nov-2019 21:38
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gchiu:

 

Having more information from the distributor a 1.6 kW heater uses about 18 1W fans to push air across the radiator.

 

So, 18Wh of electricity to move 1.6kWh of heat into the room.  

 

The 1.6 kW panel looks like the largest they sell at 2000x900 mm in size

 

 

 

 

That's for the fans. The compressor will draw far more than that.

 

 

 

Their COPs don't look any better than a conventional heat pump. The efficiency improvements gained by having smaller splits (discharge air at 25-40C not 55C, intake air at 5C not -5C) massively outweigh energy usage by fans.


gchiu

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  #2350916 10-Nov-2019 08:39
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SomeoneSomewhere:

 

That's for the fans. The compressor will draw far more than that.

 

 

 

Their COPs don't look any better than a conventional heat pump. The efficiency improvements gained by having smaller splits (discharge air at 25-40C not 55C, intake air at 5C not -5C) massively outweigh energy usage by fans.

 

 

I believe the claim is that heating to 40C using an air to water heat pump to heat fan coil radiator panels, and then convecting the heat with fans is less expensive than using a boiler to heat traditional radiators to 75C.  Do you have COP data?


 
 
 
 


SomeoneSomewhere
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  #2351223 10-Nov-2019 16:32
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I mean, sort of? A boiler is going to be <100% COP because it's just directly burning fuel - but that fuel is cheaper than electricity.

 

 

 

I was comparing to an air-to-air system, which are readily available with COPs above 4.5. If you're going to be blowing air past a coil anyway, why put an unnecessary water loop in there as well?

 

 

 

Looking around, Daikin are claiming COPs around 5 for low temperature and 3.5 for high temperature: https://www.daikin.eu/content/dam/document-library/catalogues/heat/air-to-water-heat-pump-low-temperature/Daikin_Altherma_3/Daikin-Altherma-3_Product%20flyer_ECPEN18-724B_English.pdf


gchiu

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  #2351225 10-Nov-2019 16:50
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The water loop is to move the heat into other rooms of the house. Moving air won't work.

SomeoneSomewhere
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  #2351230 10-Nov-2019 17:19
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Multiple heads is the usual answer to that one. Or a ducted system.


gchiu

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  #2351318 10-Nov-2019 22:11
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The last multihead heat pump I had installed left me no change from $10k, and that was only for three rooms.

SomeoneSomewhere
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  #2351325 10-Nov-2019 22:34
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You expect a hydronic system to be any different?


gchiu

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  #2351395 11-Nov-2019 08:45
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The water radiator was invented in 1857 or thereabouts. One would hope it would be cheaper by now.

SomeoneSomewhere
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  #2351783 11-Nov-2019 17:33
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If you want a fan forced one, it basically ends up becoming the same as a conventional heat pump except with lower pressure requirements. At least if you want comparable noise levels, power outputs, and off-coil temps (lower for better efficiency). And bigger pipes because water carries less heat per volume than refrigerant I believe.


gchiu

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  #2351903 11-Nov-2019 21:39
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I'm asking this to try and solve my quest for freedom from the grid with my small PV array and batteries. Low surface temperature radiators allow us to use water of a lower temperature for heating. Although water can be heated by vacuum tubes and flat plate collectors, that's highly dependent on the weather. The thermodynamic panels seem a much better match for these heaters. The water only is heated to 55 deg C, and heating occurs 24/7 with a large boost when the sun is shining on the panels. You don't get that boost with a standard air to water heat pump. The thermodynamic panels only have a cop of 2-3 according to Wikipedia. But you're storing all that heat in a water tank to be used at night for heating. And if you mainly do the heating during the day then it matches the PV generation.

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