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  Reply # 1757027 5-Apr-2017 14:11
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Not in any detail no. Would be interested to hear if you think it would be any better tho.


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Ultimate Geek
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  Reply # 1757032 5-Apr-2017 14:18
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SumnerBoy:

 

Not in any detail no. Would be interested to hear if you think it would be any better tho.

 

 

For sure; it's appealing to me as Dunedin is a little more restricted in day/night pricing options than Christchurch is, based on how the rates are passed on to retailers from Aurora (as I understand it).  Just trying to model it all now.





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Master Geek
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  Reply # 1757036 5-Apr-2017 14:29
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I'm guessing that the other thing to consider with a heat pump, is that since it moving heat around rather than generating it.... I assume it will work much less efficiently when it is cold outside (say at night) compared to when it is warmer during the day. If that assumption is correct (and I am no expert, so I might be wrong), then that will give you two moving targets to track against:- Spot pricing AND Outside Temperature.

 

I think there is still good potential to save money with Flick with your setup, but it'd be good to check efficiency of the heat pump at a variety of outside temperatures if you are thinking of time-shifting to save electricity costs.

 

You can then compare likely cost of running the heatpump offpeak during the day, and compare this to running it longer (due to lower efficiency) overnight but with potentially cheaper electricity. The main thing is that as long as you avoid the morning and evening peak electricity use times, then the worst spot price increases should mostly be avoided... and the few that remain SHOULD easily be covered by the savings made by being on Flick. Of course, there are no guarantees but it appears to be saving people here some money.

 

Can anyone else shed any light on this (or know whether or not I'm talking rubbish!)? Anyone with experience with HeatPump water heaters on Flick?

 

Mike

 

 

 

 


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Ultimate Geek
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  Reply # 1757040 5-Apr-2017 14:35
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miked:

 

I'm guessing that the other thing to consider with a heat pump, is that since it moving heat around rather than generating it.... I assume it will work much less efficiently when it is cold outside (say at night) compared to when it is warmer during the day. If that assumption is correct (and I am no expert, so I might be wrong), then that will give you two moving targets to track against:- Spot pricing AND Outside Temperature.

 

I think there is still good potential to save money with Flick with your setup, but it'd be good to check efficiency of the heat pump at a variety of outside temperatures if you are thinking of time-shifting to save electricity costs.

 

You can then compare likely cost of running the heatpump offpeak during the day, and compare this to running it longer (due to lower efficiency) overnight but with potentially cheaper electricity. The main thing is that as long as you avoid the morning and evening peak electricity use times, then the worst spot price increases should mostly be avoided... and the few that remain SHOULD easily be covered by the savings made by being on Flick. Of course, there are no guarantees but it appears to be saving people here some money.

 

Can anyone else shed any light on this (or know whether or not I'm talking rubbish!)? Anyone with experience with HeatPump water heaters on Flick?

 

Mike

 

 

 

 

 

 

 

 

Good points Mike - the heatump unit I'm running is rated to -20 (the company I'm using put these into Central Otago regularly and it's much colder there than Dunedin), and has a capacity of 11kW, with my load only being 8.7 (COP/efficiency is related somewhat to how hard the compressor is working).  Having said that, there's no question that the COP drops with the ambient temperature, but with your scenario of heating during the coldest part of the night, there's also less load as no-one will be taxing the HWC with showers/baths etc.  So I think your logic is still sound. 





Planning on building?  Check out my blog: https://homelessguy.nz/


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  Reply # 1757069 5-Apr-2017 14:49
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Mike, I think efficiency is a red herring here, because it's going to be the same regardless of the power company. Heat pumps do typically perform well at low temperatures, so long as they don't ice up too often.

 

The question is overnight do you pay 5-15c/kwh on Flick or 23c/kwh on another company.





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Master Geek
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  Reply # 1757075 5-Apr-2017 14:53
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I guess my rationale was to help you work out the optimum price savings for your setup:

 

Hypothetically speaking, if you found out that electricity is typically say 20% cheaper overnight, but the heatpump is only 50% as efficient overnight, then it would need to run twice as long overnight for the same temperature raise in the hot water tank... then clearly it would be cheaper to run it during the day instead. Whereas, if it was the other way round and your electricity was typically 50% cheaper overnight, but the heatpump was only 20% less efficient to run overnight, then running it overnight would be cheaper than during the day.

 

Hopefully the heatpump stats, and the pricing history for your region would let you model the approximate costs in an Excel spreadsheet.

 

Mike


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  Reply # 1757080 5-Apr-2017 15:00
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Yeah I looked at that Mike - and even asked my HP manufacturer the same question (Hot Water Heat Pumps here in NZ). The feedback was, yes the HP would operate at a lower COP during the cold night hours, but that difference would be neglible compared to the cheaper electricity. E.g. my day rate is 37c/kWh, and night is 16.5c/kWh, so the difference is more than 50%. 

 

I also asked the question about wear-and-tear, with the HP obviously having to work harder during those cold night hours. But again, the answer was it should be negligible. They are designed to work down to low temperatures, and ChCh doesn't go below zero very often anyway.


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  Reply # 1757111 5-Apr-2017 15:44
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Don't follow vendor suggestions about COP - they've a vested interest in presenting the best case while you are, of course, interested in the worst case. Plus, if they really wanted to help you, then they'd publish useful COPs with reference to the temperatures used. They don't so COPs for heat pumps are usually presented without reference to either the temperature difference or the outside temperature. This makes is difficult to know what COP you should use when modelling with specific temperature. Here's an easy to follow example of the general case: http://www.energy-without-carbon.org/HeatPumps

 

Here's another example from 2011 of specific models from Mitsubishi and Fujitsu: http://www.nrel.gov/docs/fy11osti/52175.pdf

 

It is probably realistic to model a 25% drop in the published COP. So a published COP of 4.0 would go down to 3.0.

 

Then I would model a worst case by halving the energy efficiency, a 50% drop, for running at night in winter. This would take a COP of 4 down to 2. If the cost-benefit still stacks up with a 50% drop in COP then you can be certain that you will do no worse. This 50% reduction in winter energy efficiency turns up all over the place, e.g. the quote below from 2004 US research, for continental weather conditions, i.e. -20C. This is a bit extreme even for a Dunedin winter but even at 0C many heat pumps are running closer to 2.0 than 3.0.

 

 

The climate related HSPF (Heating Seasonal Performance Factor) was found to be as much as 40% better or 50% worse than the published values depending on site winter climate.

 


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Ultimate Geek
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  Reply # 1757118 5-Apr-2017 15:52
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SumnerBoy:

 

Yeah I looked at that Mike - and even asked my HP manufacturer the same question (Hot Water Heat Pumps here in NZ). The feedback was, yes the HP would operate at a lower COP during the cold night hours, but that difference would be neglible compared to the cheaper electricity. E.g. my day rate is 37c/kWh, and night is 16.5c/kWh, so the difference is more than 50%. 

 

I also asked the question about wear-and-tear, with the HP obviously having to work harder during those cold night hours. But again, the answer was it should be negligible. They are designed to work down to low temperatures, and ChCh doesn't go below zero very often anyway.

 

 

 

 

Interesting numbers - what's your fixed daily price?  The best day/night rates I can get down here are 22c and 10c (GST incl) respectively.





Planning on building?  Check out my blog: https://homelessguy.nz/


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  Reply # 1757119 5-Apr-2017 15:53
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According to this site, power prices will be higher than average this evening. Spot price in Wellington will probably go to around 17c/kwh, plus line charges and such, from 18:00 18:30, then bounce around some. This will put the price at a little over what most people pay all the time, but it's quite a bit higher than average for Flick customers.





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  Reply # 1757120 5-Apr-2017 15:56
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nofam:

 

Interesting numbers - what's your fixed daily price?  The best day/night rates I can get down here are 22c and 10c (GST incl) respectively.

 

 

Fixed daily price is 38.33c. I am on the *Low* usage tariff as in summer I use very little thanks to no heating and solar H20 + PV. Those rates I quoted before also include GST FWIW.

 

22/10 sounds very cheap! Who is that with?


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Ultimate Geek
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  Reply # 1757139 5-Apr-2017 16:03
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SumnerBoy:

 

nofam:

 

Interesting numbers - what's your fixed daily price?  The best day/night rates I can get down here are 22c and 10c (GST incl) respectively.

 

 

Fixed daily price is 38.33c. I am on the *Low* usage tariff as in summer I use very little thanks to no heating and solar H20 + PV. Those rates I quoted before also include GST FWIW.

 

22/10 sounds very cheap! Who is that with?

 

 

 

 

Ahh, that makes sense - those prices I quoted are through these guys





Planning on building?  Check out my blog: https://homelessguy.nz/


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Ultimate Geek
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  Reply # 1757143 5-Apr-2017 16:05
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SumnerBoy:

Not in any detail no. Would be interested to hear if you think it would be any better tho.


I'm in chch
I'm sure flick would be cheaper, how much cheaper depends on when your using power. I changed from meridian a while ago and noticed significant savings. The biggest thing that irks me about day/night plans is you pay more during the day then the comparative anytime plans, but I guess that's just an averaging thing. Even so on flick we rarely see prices as high as our day rate on meridian, only in winters when the peak line charging comes in.

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  Reply # 1758175 7-Apr-2017 15:25
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Can anyone else access their "My Flick" website? It says "502 bad gateway" for me.





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Master Geek
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  Reply # 1758180 7-Apr-2017 15:32
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timmmay:

 

Can anyone else access their "My Flick" website? It says "502 bad gateway" for me.

 

 

"504 Gateway Time-out" for me

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