Alternative Technology Assn Forums

1. 

   TonyT
   Member

   The chart below shows how the COP of a heat pump varies with the temperature of the heat-source (the X-axis) and with the temperature of the output-heat (the individual lines).

   

   This chart was drawn using data from the third Chart at
   http://www.heatpumps.co.uk/graphs.htm

   plus data from the following chart found in a geothermal heating text

   

   Q1. Do the COP values in Chart 1(4) look reasonable ?

   Q2. What are the names of manufacturers who sell heat pumps with sizes that use input electricity of 1.0 to 2.4kW ?

   Posted Monday 3 Sep 2012 @ 10:28:59 am from IP #
2. 

   TonyT
   Member

   Theoretical Carnot Efficiency

   

   The goal is to use each kWh of electricity to provide the maximum kWh of heat output.

   The chart shows that the theoretical output from a heat pump will more than double if the operating temperatures are moved from operating point

   [A] heat input (from outside winter air) at 7degC with heat output at 60degC (for wall mounted radiators)

   to

   [B] heat input (from water in buried tank) at 15degC with heat output (for underfloor pipes) at 35degC

   The names of some manufacturers were provided at
   http://www.ata.org.au/forums/topic/1677#post-15754

   Q1. What is the highest COP achieved from a commercially available heat pump operating with input temperature 15degC and ouput temperature 35degC ?

   Q2. Who makes it and where can I buy it ?

   Posted Monday 3 Sep 2012 @ 8:19:22 pm from IP #
3. 

   Bushwalker
   Member

   Interesting stuff.

   I guess for [B] you have to make your underground store large enough and give it good capability to lose heat to the surrounding soil/rock or you will freeze it in winter and/or boil it in summer. There are stories of people in the US freezing lakes with their GSHP hooked into a local lake.

   Don't know about brands of heatpumps. The commercial ground source systems I have seen (Waterfurnace, link below) have not been cheap, but perhaps an individual HP without added installation and design costs might be more reasonable?

   http://www.geoexchange.com.au/water_to_water.aspx

   Posted Tuesday 4 Sep 2012 @ 12:55:25 am from IP #
4. 

   TonyT
   Member

   Bushwalker

   The brilliant principles are being used at Mt Best
   http://mtbest.net/heat_pump.html

   Solar heat is collected at low temperature so the collectors do not need costly vacuum insulation.
   The heat is stored in water held in a tank that is buried so that costly insulation is not needed.

   At low temperature (? 15degC) collectors absorb more than 90% of the incoming solar heat.
   This high efficiency needs the least area of collectors which minimizes their cost.
   Because they operate at low-temperature the solar-collectors are made simply and at least-cost using coils of poly-pipe.

   The heat pump sources heat from warm water (? 15degC in the buried tank) and supplies that heat into the building at the lowest possible temperature (? 35degC).
   With a small temperature difference a heat pump has a high Coefficient of Performance (? 5.9). It delivers the most heat from using the least number of kWh of electricity.

   Because under-floor hydronic heating is using the largest practical area (the floor) as a radiator, the temperature of the water can be at the minimum that is needed to heat the room (? 35degC). A floating floor can be the radiator.

   If the under-floor heating pipes are not encased in concrete, the radiator can have low thermal mass. The room temperature can be changed quickly and hence the room does not need to be heated 24/7.

   http://www.ata.org.au/forums/topic/2275#post-30879
   http://www.ata.org.au/forums/topic/4115/page/2#post-30795

   Posted Tuesday 4 Sep 2012 @ 3:11:41 am from IP #
5. 

   Bushwalker
   Member

   Hi Tony,

   I get that. I think my point was that you might still have to match the size of the storage tank to the expected kw draw from the house in times of low solar activity. I don't know if Mt Best did the calculation in choosing the size of their underground tank (probably), but unless your system is going to draw the same heat per hour from the stored water it might be best to do the calculations.

   It is very important to note, that a 1 kW heat pump is enough to warm up our entire @20 square house ONLY because the house is well insulated and has double glazed windows.

   [..]

   By monitoring heat pump parameters we established that our house needs 16.3 Watt per square metre of living area to maintain the interior temperature 12°C higher than outside.

   BW

   Posted Tuesday 4 Sep 2012 @ 4:29:18 am from IP #
6. 

   Solgen
   Member

   I did a lot of heat pump testing when I worked for the Electricity Technology Centre. At that time Quantum heat pumps used flat plate collectors and we typically had COP's of 2 to 2.5. With pool heating using conventional (air source) coils we would often get COP's of up to 5.0. The difference is the temperature of the water, heat pumps are fantastic for heating water to low temps (30deg) but once you start to push to higher temperatures, the performance drops off quickly as the temp differential between the hot gas in the condenser and the water becomes smaller.
   In contrast tests on Water Furnace ground source heat pumps consistently produced COP's of 5 to 6, however this was heating air not water. They were very good but expensive to install with drilling rigs, etc required.

   Posted Tuesday 4 Sep 2012 @ 7:50:45 am from IP #
7. 

   TonyT
   Member

   Thanks Solgen

   Your tests seem to confirm the data in the first chart at
   http://www.ata.org.au/forums/edit.php?id=31001

   Posted Tuesday 4 Sep 2012 @ 9:49:08 am from IP #
8. 

   TonyT
   Member

   The chart below shows the performance and COP data for the Danfoss SC21G heat pump.

   http://www.servipartes.com.mx/uploads/pdf/Danfossrefrigeracionselection.pdf
   http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/06/SC21G_R134a_220V_50Hz_06-04_Cd44l802.pdf

   This heat pump is used in one brand of domestic heat pump hot water service.

   

   Posted Wednesday 5 Sep 2012 @ 9:55:54 am from IP #
9. 

   TonyT
   Member

   The Japanese Sanden heat pump uses CO2 for the refrigerant.

   The Sanden literature claims a COP of 4.5.

   http://www.sanden.com.au/Consumer/Hot-Water-Heat-Pump.php

   Recently the Sanden has become available in Australia at a price similar to the Siddons

   http://www.enter-shop.com.au/catalogue/c4/c21/p933

   Can anyone provide Charts that show how the COP of a Sanden varies with the input temperature and with the output temperature ?

   Posted Monday 10 Sep 2012 @ 10:04:07 am from IP #
10. 

    Jeffbloggs
    Member

    Hey TonyT
    Have a look at the brushless inverter DC compressors (HP) from http://www.masterflux.com/

    I note that a smaller temperature delta increases COP, but with it you also need to increase the mass (volume) of the sun heated water in the poly tubes to achieve the same net heat gain. Increased mass/volume also increases the container surface area and heat loss at night. Will a bigger dimensioned system running at a low temp delta be as effective as a relatively small system running at a a high delta?

    BTW we never did finish that demo house thermal analysis we started? I'll have to look it up again.

    Posted Wednesday 12 Sep 2012 @ 10:59:33 am from IP #
11. 

    TonyT
    Member

    When will our American friends move away from Btu's to measure energy (and from "acre feet" to measure volumes of water) ?

    Posted Wednesday 12 Sep 2012 @ 11:19:58 am from IP #
12. 

    Jeffbloggs
    Member

    lol
    Maybe when we stop calling them friends and welcome them into the 21st century?
    They are professionals at keeping their population dumbfounded by the maths of currency and conversion... I think SI units are a curse word in the US, thats why they don't use them. Use this to convert: http://www.wolframalpha.com/

    Have you tried using their telephone system? The number can change according to what telco you are using and what state/county prefix you are calling from....it's sometimes easier to call via an international route than direct.

    Posted Wednesday 12 Sep 2012 @ 11:32:56 am from IP #
13. 

    TonyT
    Member

    A fantastic conversion tool !

    We will be using their phone system for 6 weeks from Sep 23.
    Hopefully friends will tutor us.

    I started this thread to discuss COP of heat pumps.

    Posted Wednesday 12 Sep 2012 @ 11:48:22 am from IP #
14. 

    munter
    Member

    Hi Tony,
    There is some useful COP information in this brochure from Stiebel Eltron.

    http://www.stiebel-eltron.co.za/downloads/WWK_300%20A-AP%20Brochure.pdf

    We currently have one of these running at our place but I haven't done any measurements on its power consumption nor heat production so I can't comment on whether its performance matches the curves.

    Posted Thursday 13 Sep 2012 @ 3:42:17 am from IP #
15. 

    TonyT
    Member

    Thanks munter

    The Stiebel chart shows the COP at 7degC is 2.3 and the COP is 3.1 at 15degC
    http://www.stiebel-eltron.co.za/downloads/WWK_300%20A-AP%20Brochure.pdf

    Compare 2.1 and 2.4 in the chart at
    http://www.ata.org.au/forums/topic/4384#post-31076

    and 2.7 and 3.1 in first chart at
    http://www.ata.org.au/forums/topic/4384#post-31001

    Still looking for COP data for Sanden that uses CO2 for its refrigerant.

    Posted Thursday 13 Sep 2012 @ 9:53:08 am from IP #
16. 

    TonyT
    Member

    Jeffbloggs

    Largest compressor I can find at

    http://www.masterflux.com/

    is

    http://www.masterflux.com/userimages/CASCADE17-0306Y3_Data_Sheet.pdf

    With evaporator at outside temperature of 7degC and heat output from condenser at 55.4degC, specs say it delivers 666W of heat at 4200rpm with COP of 2.51

    I am hoping to find 2,000W to 4,000W of heat and to match or exceed the COP of 4.5 claimed in the Sanden literature.

    Posted Friday 14 Sep 2012 @ 10:26:16 pm from IP #
17. 

    IrishPete
    Member

    Maybe the wrong place to post this question (but when did that ever stop anyone?) but I suspect my Quantum heat pump has been underperforming for several months. Living in an area slight colder than Canberra, it's really hard to know, but I am sure that in previous winters it did not run all day, but would reach its temperature than cut out. (I have it on a timer, so I don't know if it would run continuously if I unplugged the timer).

    I've read that they sometimes they need re-gassing, but with a $150 or more callout charge to my area, is there any way I can test it myself? Either the gas or just its general performance?

    It's running off solar panels (when the sun shines) and not much else electric runs during the day, so I haven't been too concerned about the electricity consumption as the solar largely covers it (I'm on a crappy FIT, not one of the good ones).

    Peter

    Posted Friday 14 Sep 2012 @ 11:34:26 pm from IP #
18. 

    TonyT
    Member

    1. Try unplugging the timer for 24hrs and check the Quantum ? hourly and record if it is running.

    2. Use the electricity meter. Record the time and the meter reading and what is running.

    For a period when only Q is running divide kWh used by hours elapsed to calculate kW being used by Q and compare with specs for Q

    Posted Saturday 15 Sep 2012 @ 3:40:52 am from IP #
19. 

    rockabye
    Member

    IP, I have a Quantum 270L which lost its gas on two occasions. Both times were loose connections which I think occurred during transport. When it arrived it was damaged at the base where it had been dropped off the pallet. If you click on my name at the left it should open my webpage where there are photos and details of the problem.

    Basically it should not be running all day. If you take off the top cover you should be able to see the sight glass which if it has bubbles in it means it is low on gas. My hws is on a separate digital meter and in winter can still use 9kWh/day when some occupants have long showers and clothes are washed. Summer usage is around 2kWh/day.

    Posted Saturday 15 Sep 2012 @ 5:11:24 am from IP #
20. 

    IrishPete
    Member

    thanks Rockabye - that's really helpful. Do you recall how much the regas cost?

    Peter

    Posted Saturday 15 Sep 2012 @ 6:38:48 am from IP #
21. 

    rockabye
    Member

    From memory it was about $250 some 4 years ago Peter.

    Posted Saturday 15 Sep 2012 @ 7:00:29 am from IP #
22. 

    jtb
    Member

    I briefly looked into heat pumps for hydronic heating and HWS as i have no gas in street and cloudy winters rule out solar. Airsourced HPs for hydronics have a reasonable start up price (Skyline Energy) but I was worried the COP would not hold up during long cold winters. Ground sourced Geothermal HP had too high a start up.

    No one until now has suggested water sourced from buried tank. I am interested in how it pans out for TonyT.

    I am concerned that the benefit of lower output water temp (better COP) would be offset by having to have it run for long periods of the day and thus using electricity out of offpeak times (in SA).
    Q - is your buried tank solely for the Heat Pump?

    Posted Tuesday 18 Sep 2012 @ 11:24:36 am from IP #
23. 

    TonyT
    Member

    Continuing from
    http://www.ata.org.au/forums/topic/4384#post-31362

    the COP values for a heat pump that uses CO2 for its refrigerant is included as the purple-coloured line with asterisk-markers in Chart 1(5) below

    .

    

    .

    Domestic hot water is heated to 60degC to kill micro-organsims.

    The performance of a non-CO2 heat pump (e.g. Siddons) when it delivers heat at 60degC is shown by the line "Output Heat at 60degC". The line gives the COP value (Y-axis) for each input temperature (X-axis).

    The performance of a CO2 heat pump (e.g. Sanden) when it delivers heat at 60degC is shown by the line "CO2 Output Heat at 60degC".

    For heat pumps that are delivering heat at 60degC, the Chart shows that if the heat is collected at zero degC (e.g. from outside-air, at night in winter) this CO2 heat pump has COP=3.5 compared with COP=2.4 on the line for this non-CO2 heat pump.

    The different COP values mean that the number of kWh of electricity (and the annual running cost $) used by the non-CO2 heat pump will be
    100 x 2.4 / 3.5 is 69%
    of the kWh (and $) used by the CO2 heat pump.

    The Chart shows that if the heat is collected from warmer-outside-air at 10degC this CO2 heat pump has COP=4.2 compared with COP=2.8 for this non-CO2 heat pump.

    A COP of 4.2 means that the use of one kWh of electricity delivers 4.2kWh of heat.

    The Chart at
    http://www.ata.org.au/forums/topic/4384#post-31076

    shows that the Danfoss SC21G heat pump has lower COP values e.g. COP=1.8 when it collects heat at zero degC and COP=2.2 when it collects heat at 10degC.

    Posted Sunday 17 Mar 2013 @ 9:09:51 pm from IP #
24. 

    ML
    Member

    Apparently you can buy the siddons with the same refrigerant as the sanden for an extra $400. It sounds like that would be worth it from your calculations?

    Posted Monday 18 Mar 2013 @ 11:24:00 am from IP #
25. 

    TonyT
    Member

    ML

    If the COP values for the Siddons versions "with" and "without" CO2 refrigerant match with the corresponding values in the Chart at
    http://www.ata.org.au/forums/topic/4384#post-39596
    then using the "with-CO2" version will reduce the annual electricity cost by about 30%.

    The litres of hot water and hence the $ of water-heating-electricity used in one year will determine the number of years needed to recoup the additional cost of $400.

    Also:
    New anti-pollution legislation may have dramatically increased the cost to re-gas all "without-CO2" systems.

    Posted Monday 18 Mar 2013 @ 9:31:11 pm from IP #
26. 

    TonyT
    Member

    Correction:

    A heat pump that uses CO2 as its refrigerant has a higher COP.
    This means that a CO2-heat-pump pumps more heat per kWh of electricity and has a lower running cost than does a non-CO2 heat pump.

    In
    http://www.ata.org.au/forums/topic/4384#post-39596

    The sentence should read:

    The different COP values mean that the number of kWh of electricity (and the annual running cost $) used by the CO2 heat pump will be
    100 x 2.4 / 3.5 is 69%
    of the kWh (and $) used by the NON-CO2 heat pump.

    Posted Sunday 21 Apr 2013 @ 2:22:52 am from IP #
27. 

    TonyT
    Member

    Air at minus 40degC can be the source of heat for the CO2 heat pump at
    http://www.r744.com/news/view/4223

    Posted Thursday 16 May 2013 @ 9:19:32 pm from IP #
28. 

    TonyT
    Member

    A first quick look at the data that we have collected this winter (2013) from our heat pump indicates that in August 2013 its COP may be as low as a disappointing 1.8 rather than the 2.6 that we had anticipated for outside overnight average temperatures of about 5degC.

    On most August nights it has rained or the outside air has been at close to 100% relative humidity.

    Q1. Does the COP of a heat pump reduce when its heat-source is air with high humidity ?

    The Specific Heat for water is 4.184kJ/kg per degC
    The Specific Heat for air is 1.0 kJ/kg per degC

    Q2. If air that contains water holds more heat than does dry air, why would a heat pump extract LESS heat from humid air ?

    Q3. Does the following Chart look to be correct ?

    .

    

    .

    The following link may provide some of the answers:
    http://www.consumer.org.nz/reports/heat-pumps/heat-pump-faqs

    .

    Posted Wednesday 28 Aug 2013 @ 8:49:26 pm from IP #
29. 

    StephenF
    Member

    Hi Tony, what type of pump did you end up getting?

    I have no idea about humidity, could it be something like as you suck heat from humid air moisture condenses on your external heat exchanging coils (or whatever they are called) and then as they evaporate from fan forced air, they rob a little more of the heat/energy, reducing the heat left for the exchanger? Effectively making the system operate at a slightly cooler temp than the equivalent temp dry air?

    Posted Wednesday 28 Aug 2013 @ 11:29:54 pm from IP #
30. 

    TonyT
    Member

    StephenF

    The items are listed at
    http://www.ata.org.au/forums/topic/2135#post-18652

    Posted Thursday 29 Aug 2013 @ 10:18:49 am from IP #

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