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Green Building Bible, Fourth Edition
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    •  
      CommentAuthordjh
    • CommentTimeJan 15th 2015
     
    topher wrote: "SteamyTea,

    I don't agree. . . . .

    I got this quote from Wikipedia ...

    It is perfectly fine to measure heat output in kWh."

    Steamy's point wasn't about the units of measurement. It was, as he said, that electrical energy is different to thermal energy. Try looking at wikipedia:

    http://en.wikipedia.org/wiki/Exergy and perhaps http://en.wikipedia.org/wiki/Energy_quality
    • CommentAuthorEd Davies
    • CommentTimeJan 15th 2015
     
    Topher's description of CoP looks fine to me, I don't understand what the fuss is about.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 15th 2015
     
    I was just commenting on the below statements. I think it can sometimes lead to confusion if a distinction between electrical energy and thermal energy are not separated (it can lead to a perpetual motion machine if your not careful :wink:).
    Posted By: topherSo if your heat pump has a COP of 3.0, you put in 1 Kw and get the equivalent of 3 Kw of heat out. If you have a COP of 4.0, you put 1 Kw in and get equivalent of 4 Kw out, that is 25% better. Tweaking will make your system work better and you will be able to get closer to your theoretical COP.

    Or have I got the whole thing wrong?
    :wink:
    • CommentAuthorEd Davies
    • CommentTimeJan 15th 2015
     
    Dunno, but by page 9 of a GSHP thread I imagine you can reasonably assume that readers have at least a hazy idea of what a heat pump is and which energy flows are likely to be being measured.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 15th 2015
     
    I would hope so too
    • CommentAuthortopher
    • CommentTimeJan 16th 2015
     
    Chaps,

    I think we are all in agreement. Clearly electrical energy is different to heat energy, but fortunately both can be measured in Kw.

    I was just concerned that Boggy might be thinking he can achieve the max possible efficiency by tweaking his heat pump. True, but he might be able to get even more by choosing a heat pump with a greater COP, and getting the heating capacity to match his house.

    Now for something completely different. I too have a kWh meter solely measuring heat pump consumption. I have readings noted down. What can I learn from the data?

    Regards,...........Topher.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 16th 2015
     
    How often do you read the meter.
    You can plot the meter readings against external temperature if you have enough readings.

    Just knowing the total kWh (how big the box of energy is) is of little use in itself.
    • CommentAuthorcjard
    • CommentTimeJan 16th 2015
     
    You could read this interesting 110 page report and work out what data they collected, collect the same and apply similar analyses?

    https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/48327/5045-heat-pump-field-trials.pdf
    • CommentAuthortopher
    • CommentTimeJan 16th 2015
     
    Thanks chaps. Will do as you advise.
    • CommentAuthorskyewright
    • CommentTimeJan 16th 2015 edited
     
    • CommentAuthorMikel
    • CommentTimeJan 16th 2015
     
    We are participating in a DECC sponsored trial of control systems for heat pumps. I get weekly data sent to me for the following parameters:

    Time
    boiler out pipe temperature
    boiler in pipe temperature
    zone 1 temperature
    temperature sensor 1
    temperature sensor 2
    temperature sensor 3
    temperature sensor 4
    external temperature (I think this comes from the nearest MetOffice station)
    heat pump power consumption
    heat pump energy consumption
    whole home power import
    whole home energy import
    BINARY_SENSOR_5_METER_POWER
    BINARY_SENSOR_5_METER_ENERGY (this is the heat meter reading)
    DEVICE_STATUS_1_ON_OFF_SWITCH
    heating control zone 1
    user setpoint zone 1

    In addition, I record the electricity meter reading for the heat pump and whole house twice a day, plus daily PV generation and solar thermal max hot water temperature reached. In addition, I separately record the electricity consumption of the heat pump for hot water generation. I also record the number of times the immersion heater is used and try and estimate how electricity that is using (probably better done from element power and time on).

    We have had data from last January (when the electricity meter on the heat pump was installed), last February (when the heat meter installed).

    We ran the system using weather compensation up to the end of February and then switched to the trial control system. So I only have most of last February's data for the original system, making comparison with any improvement seen from the trial a little bit tricky.

    However, we are seeing SPF (calculated from heat output divided by GSHP electricity consumed) going from 3.2 for the original system to 3.5 for this last month.
    • CommentAuthortopher
    • CommentTimeJan 16th 2015
     
    SteamyTea,

    I have kWh readings weekly when I am at the house, which is about 50% of the time. When absent, the internal temperature is set to about 13 degrees. I guess I would need some average ambient temperature readings. But from recent posts, I have discovered that I might get a 'heat meter' the would accurately measure the output of the heat pump.

    So far I have discovered the Kamstrup 402. Its going to cost quite a bit. So I might not do it.

    Any suggestions very welcome.

    Regards,............Topher.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 16th 2015
     
    Not had much to do with heat meters, but if they have the facility to log data every few seconds/minutes, then that is a bonus.
    All a heat meter does is measure the temperature difference and the velocity of the mass of water flowing. Then multiplies the temp difference by the total mass over the sampling period and multiplies it by the specific heat capacity. That is why DECC are collecting data from MikeL, it checks his HP and the heat meter. If there is a big difference then something is wrong.

    You can get some weather data from your nearest Weatherunderground station, best to see what sort it is, Davis Pro's are the best (maybe called a Davis 2 I think). Then you can correlate your energy usage and the external temp. Won't tell you everything, but is useful.
    • CommentAuthorMikel
    • CommentTimeJan 17th 2015
     
    I can confirm that the heat meter fitted to our GSHP records at one minute intervals. Don't know whether other intervals are available. Since we are on a DECC sponsored trial, it is a DECC specified heat meter.

    It seems to me that you would want the meter to sample at fairly short intervals to get the accuracy.
    • CommentAuthorEd Davies
    • CommentTimeJan 18th 2015
     
    Posted By: SteamyTea…and multiplies it by the specific heat capacity
    Does that get set on the heat meter, somehow? For a district heating system they use more-or-less pure water (doesn't need freeze protection, presumably) so it's well known but for a GSHP with brine or, particularly, for a solar thermal system full of anti-freeze it can be a lot less (half?)
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 18th 2015
     
    No idea Ed.
    Don't know much about them. I would hope that it is sorted out somehow.
    • CommentAuthorMikel
    • CommentTimeJan 18th 2015
     
    For the location of heat meters for heat pumps, see p112 in the reference given by skyeright.

    You may be correct with respect to the solar thermal system but it seems to me that the heat meter is on the central heating side, which is water and corrosion inhibitor.
    • CommentAuthorMikel
    • CommentTimeJan 18th 2015
     
    Just found the DECC report on heat meters.
    https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/48043/1386-heat-metering-rhi-gastec-at-cre-ltd.pdf

    Note that for solar thermal systems the heat meter is calibrated to take the anti-freeze mixture into account.
    • CommentAuthorEd Davies
    • CommentTimeJan 19th 2015
     
    Posted By: Mikelbut it seems to me that the heat meter is on the central heating side,
    Good point, though slightly perverse in that the ground-loop side is the “renewable” bit; it doesn't include the electrical energy. Also, thanks for the link.
    • CommentAuthorskyewright
    • CommentTimeJan 19th 2015 edited
     
    Posted By: SteamyTeaYou can get some weather data from your nearest Weatherunderground station, best to see what sort it is, Davis Pro's are the best (maybe called a Davis 2 I think).

    Davis Vantage Pro 2 (sometimes abbreviated to VP2).

    However (at the risk of veering OT) if it's only outdoor temp you are interested in then a much cheaper one will probably only be marginally poorer if you can site it well &/or if you build it's temp sensor a proper housing (think Stevenson screen). It's wind & rain measurements, & a superb console, where the Davis mainly scores over cheaper models, in both precision & longevity. The Davis station can also be extended in various ways if you have a deep enough pocket.

    Normal service now resumes...
    • CommentAuthortopher
    • CommentTimeMay 29th 2015
     
    Report Number 32. 29 May 2015

    In previous reports I have complained about 3 or 4 leaks caused by brass fittings cracking and leaking primary or secondary fluid. I believe it was caused by over-enthuistic tightening, the installer says, as you might expect, that the fittings were defective. The most recent leak in the primary caused the pump to stop because of low flow, but more significantly the liquid damaged the chipboard flooring and the heat pump began to list to one side.

    I had the heat pump and inertial cylinder disconnected, the floor repaired with a better quality product, and the heat pump and cylinder re-installed. One extra bit of equipment was added - a heat meter. It has an ultrasonic device to measure flow, and two sensors that measure flow and return temperature. I gave the system a quick test and everything works fine and I can see that it had produced one or two kW of heat output.

    In the winter I will note the readings and hopefully be able to measure the COP of the heat pump. I also have a data logger, and hope to use that to give a graphical display of heat over time.
    • CommentAuthortopher
    • CommentTimeOct 6th 2015
     
    Report Number 33. 6 October 2015.

    As it was a bit chilly, I put the heat pump on for two days. It consumed 29.7 Kw/h of electricity. It gave 117 Kw/h of heat output as measured with my new heat meter. This gives a COP or efficiency of 3.94. Or I could say, I bought 29.7 Kw/h from EDF. I got 87.3 Kw/h free from the ground.

    Seems OK to me. What do you think?
    • CommentAuthorDarylP
    • CommentTimeOct 6th 2015
     
    free is good! :wink: how much was the 29.7 from EDF?
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 6th 2015
     
    Posted By: topherKw/h
    It's kWh

    CoP of 4 is good, ground is still warm though. Had it rained recently?
    • CommentAuthorringi
    • CommentTimeOct 6th 2015
     
    Posted By: tophersumed 29.7 Kw/h of electricity. It gave 117 Kw/h of heat output as measured with my new heat meter. This gives a COP or efficiency of 3.94. Or I could say, I bought 29.7 Kw/h from EDF. I got 87.3 Kw/h free from the ground.

    Seems OK to me. What do you think?


    Not much better then using storage heaters, so paying less to EDF for more power.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 6th 2015
     
    Posted By: ringiNot much better then using storage heaters, so paying less to EDF for more power.
    ?
    My E7 night rate is about 8p/kWh, day rate about 18p/kWh and think the standard rate is around 14 to 15p/kWh.
    So only about half price.
    • CommentAuthorringi
    • CommentTimeOct 6th 2015
     
    What if the cost of the ground source heat pump was spent on better insulation etc......

    The COP is also likely to be lower when it is colder as the ground would be cooler by then due to the heat being taken out. Ground source heat pumps just seem to give too many issues and not work in a predictable way.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 6th 2015
     
    Posted By: ringiWhat if the cost of the ground source heat pump was spent on better insulation etc......
    Assuming it is a 'slinky' installation rather than a borehole (these are the best), how about if you covered the same area in PV, what would that yield in the winter and what would it cost (putting aside the MCS/FiT nonsense for a while).
  1.  
    Posted By: ringigive too many issues and not work in a predictable way.


    This is the 10th season mine has been in use and it has been entirely predictable so I'm not sure what you mean. I have a borehole, though, rather than "slinkies". COP is consistent from year to year and the energy savings have fully covered the cost of the installation (this happened around 3-4 years ago). I have an old house and there are technical limits to how much insulation can be added (really, not much more than 25mm, though air leakage issues have been addressed). My GSHP is water-to-air, as we need cooling in the summer and this kind of system is essentially simpler than water-to-water. The only maintenance required is to replace the air filter on a regular basis.

    Paul in Montreal.
    • CommentAuthorringi
    • CommentTimeOct 6th 2015
     
    In the UK it has been found that often they don't work as claimed due to the quality of the install or design. No one will provide an insurance back 100% statement about what COP the complete insulation will give.

    I expect that a water to air system would be more predictable (provided there a big ducts) as there are a lot less issues with sizing of radiators etc. (Or carpets on UFH)
   
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