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Retrofitted heat pumps.

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    #32
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    Latro wrote: »
    The system I have is "trying" to maintain constant delta of 5 by modulating compressor speed and water pump speed.

    It cant be changed afaik and it has something to do with the amount of refrigerant in the system. But in other systems this can be adjusted.

    The water flow fluctuates between 30 and 40 degrees depending on external air temperature. It is using weather compensating curve.
    The HP doesn't care what the temperature is inside the house. It was up to me to find lowest possible curve to achieve the comfort I wanted.

    It took about 1-2 weeks for me to fine tune it. IMO it is better way of control over internal thermostats because the HP knows it has to increase or decrease flow temps before the cold even reaches your walls.

    It was sort of novelty few years ago but now it is becoming mainstream and on any foreign forum experienced users or installers recommend this form of control as the most efficient, in particular when underfloor radiator is used because of big thermal inertia it has.
    With internal thermostats the lag between temperature drop and response could be quite big.

    That's very informative and makes perfect sense especially keeping the deltaT as low as possible because it results in a higher mean rad temperature or the the same mean temperature with a lower inlet temperature, I used a deltaT of 7C in my case above which gave me a, (39+32)/2)-21, a "14.5"deg rad with a output factor of, (14.5/50)^1.3, 0.2 or 20%. Using a deltaT of 5C (just 2C lower) then I would get the exact same output with 38C in and 33C out rad temperature, 1 deg C mightn't seem much of a reduction in the HP temperature but it results in a 2 to 3% increase in the HP efficiency.

    Its very easy to use the correction formula above that I use for rad output but I am including a link to read off those correction factors (based on "50 deg" rads) https://www.aelheating.com/blog/how-to-calculate-delta-t/


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    #33
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    agusta wrote: »
    John,im not quite into the maths but more the end result.
    With a heat pump the heating is always on pretty much controlled by the thermostats.So the house and hot water is pretty much at the same temperature 24/7
    The only way you can compare 0il/gas to a heatpump is if the oil/gas boiler is constantly on,with heating and hot water only controlled by the thermostats
    Example
    I have a high efficiency oil boiler on my books.house 2,700 sq ft.boiler never turned off.house b rated,approx oil usage a little over 4000 litre pa

    My brothers house is 2,600 sq/ft, A rated,air to water heat pump,cost per year 800 euro approx.

    That's a huge difference between the two house energy needs, you are inputting ~ 36,000 kwh/heating year say ~ 150 kwh/day, 6.25 kwh/hr. A 9 kw HP should cover your needs?. Without any house mods you should save ~ €1446/year, a tidy sum. HP running cost on full price elect @ €0.16/kwh and a COP of 3.5, ~ €1645/year vs ~ €3092 on oil. You can possibly save more by installing a night rate meter but you would have to do the sums on that as the day rate units are more expensive than when on the single tariff.


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    #34
    lucast2007us
    Registered Users Posts: 801 ✭✭✭lucast2007us


    I have been told that the running cost of a heat pump on my electricity bill would be about 2,000 euro a year.

    Sounds very steep any truth to this?


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    #35
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    lucast2007us wrote: »
    I have been told that the running cost of a heat pump on my electricity bill would be about 2,000 euro a year.

    Sounds very steep any truth to this?

    What are you using at the moment? oil or gas? and any idea of litres of oil used/year or sample of gas bills which show the Kwh consumed. What size house??. Without that sort of info its impossible to even hazard a wild guess.


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    #36
    lucast2007us
    Registered Users Posts: 801 ✭✭✭lucast2007us


    What are you using at the moment? oil or gas? Oil

    and any idea of litres of oil used? Probably 1200 litres

    What size house?? 4 bed detached.


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    #37
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    lucast2007us wrote: »
    What are you using at the moment? oil or gas? Oil

    and any idea of litres of oil used? Probably 1200 litres

    What size house?? 4 bed detached.

    That's very (good) low oil consumption for for a 4 bed, I use 1500 litres in a "4"
    bed.... 3+ converted attic.
    based on my last fill of oil in Dec, €0.77/litre then your oil cost is £924, if you install a heat pump and achieve a COP of 3.5 (read "Latro's" recent posts on here) then the HP running costs based on full cost elect should be ~ €492/annum, it would be almost thermodynamically impossible to spend £2000/annum based on your usage and assuming a condensing (or even a non condensing) boiler @ 85% efficiency. You would'nt even spend that (£2000) even with all electric heating!.


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    #38
    Latro
    Registered Users Posts: 207 ✭✭Latro


    lucast2007us wrote: »
    What are you using at the moment? oil or gas? Oil

    and any idea of litres of oil used? Probably 1200 litres

    What size house?? 4 bed detached.

    1200l of oil that's about 12000kWh of heat energy.
    At 80% boiler efficiency your house "consumes" 9600kWh.

    To produce same amount of heat energy with heat pump it would cost you:

    9600kWh / 3.3COP * €0.16 = €465


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    #39
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    Latro wrote: »
    1200l of oil that's about 12000kWh of heat energy.
    At 80% boiler efficiency your house "consumes" 9600kWh.

    To produce same amount of heat energy with heat pump it would cost you:

    9600kWh / 3.3COP * €0.16 = €465

    Latro, I am after throwing away £27!.


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    #40
    agusta
    Closed Accounts Posts: 1,590 ✭✭✭agusta


    It will depend on the energy rating of the house,insulation,air tightness.If it doesent pass the minimum requirement then there is no point putting in air to water and you also will not qualify for the grant.If the house passes min requirement i would think running cost 800 approx.Certainly no where near 500
    Air to water does not work the same as oil.Air to water is pretty much always on.Oil is not,the time clock for oil in most houses is turned off more than it is on.You cant quite compare air to water costing with oil to any degree of accuracy in this way


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    #41
    Latro
    Registered Users Posts: 207 ✭✭Latro


    agusta wrote: »
    ... Certainly no where near 500...


    Cost for Oct, Nov, Dec. 200sqm build to pre 2008 regulations+upgraded attic insulation.

    Yellow bars are cost for any given day, grey curve is average external temperature, on the bottom estimated cost for whole month.



    73nznn.png





    359bj2e.png
    25up0ms.png
    vrleW2Z


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    #42
    agusta
    Closed Accounts Posts: 1,590 ✭✭✭agusta


    How many people live in your house..,what is your hot water requirement..what temperature is the hot water


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    #43
    Latro
    Registered Users Posts: 207 ✭✭Latro


    agusta wrote: »
    How many people live in your house..,what is your hot water requirement..what temperature is the hot water


    2 adults and 9 years old child.

    This graph does not include domestic hot water. It covers space heating only.


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    #44
    agusta
    Closed Accounts Posts: 1,590 ✭✭✭agusta


    How is your hot water heated then may i ask..,also why is the air to water not heating the hot water..


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    #45
    Latro
    Registered Users Posts: 207 ✭✭Latro


    agusta wrote: »
    How is your hot water heated then may i ask..,also why is the air to water not heating the hot water..


    Power shower+instant water heater in the kitchen.


    I wanted to see how it performs for heating only and it stayed that way for now but I could switch to HP DHW any time.


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    #46
    agusta
    Closed Accounts Posts: 1,590 ✭✭✭agusta


    Grand,when you had the hp heating the cylinder ,what temperature did it heat the cylinder to.Also what difference did this make to the monthly figures


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    #47
    Latro
    Registered Users Posts: 207 ✭✭Latro


    agusta wrote: »
    Grand,when you had the hp heating the cylinder ,what temperature did it heat the cylinder to.Also what difference did this make to the monthly figures


    When I tested it right after the HP was installed in the summer daily cost for DHW was 15-20 cents but than again we are only a family of 2 and 1/2.
    We have 280l cylinder and there is no way we would use all of that each day.
    The water temperature was set at 50 degrees.


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    #48
    agusta
    Closed Accounts Posts: 1,590 ✭✭✭agusta


    The only thing if you do switch the cylinder back to the hp,then the temperature has to be set higher.water heated to only 45-50 degrees bring in the risk of legionnaires disease.
    Any idea what would it cost for 2 adults 4 children,say using 50 litres each per day with the water temp at 60 degrees using a hp..


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    #49
    Latro
    Registered Users Posts: 207 ✭✭Latro


    agusta wrote: »
    The only thing if you do switch the cylinder back to the hp,then the temperature has to be set higher.water heated to only 45-50 degrees bring in the risk of legionnaires disease.
    Any idea what would it cost for 2 adults 4 children,say using 50 litres each per day with the water temp at 60 degrees using a hp..

    The heat pump has connection to the immersion heater inside the cylinder and it performs anti legionella cycle once a week or you can boost it to 65C with built-in heater too.

    To heat up 300l of water from 20C to 50C you need:
    300l*4*30Celsius/3412=10.55kWh

    You would need to add some extra for heating up copper cylinder mass and some losses to pipes and insulation but the number shouldn't be much bigger. Probably extra 15-20%

    To produce 10.55 kWh of heat energy will roughly cost you:
    with oil 1 euro (efficiency factor 0.8 and oil price 80cents/l),
    with immersion heater 1.70 (efficiency 1, electricity 16c/kWh),
    with hp 0.51 (efficiency 3.3, electricity 16c/kWh) in the summer efficiency factor would be much higher here probably around 4.5 so it would make it even cheaper.


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    #50
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    Latro wrote: »
    The heat pump has connection to the immersion heater inside the cylinder and it performs anti legionella cycle once a week or you can boost it to 65C with built-in heater too.

    To heat up 300l of water from 20C to 50C you need:
    300l*4*30Celsius/3412=10.55kWh

    You would need to add some extra for heating up copper cylinder mass and some losses to pipes and insulation but the number shouldn't be much bigger. Probably extra 15-20%

    To produce 10.55 kWh of heat energy will roughly cost you:
    with oil 1 euro (efficiency factor 0.8 and oil price 80cents/l),
    with immersion heater 1.70 (efficiency 1, electricity 16c/kWh),
    with hp 0.51 (efficiency 3.3, electricity 16c/kWh) in the summer efficiency factor would be much higher here probably around 4.5 so it would make it even cheaper.

    COP numbers from a Kingspan unit(s) attached.


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    #51
    lucast2007us
    Registered Users Posts: 801 ✭✭✭lucast2007us


    John.G wrote:
    COP numbers from a Kingspan unit(s) attached.


    Hey John looks good how can you tell me how much did your heat pump cost with labor costs etc?


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    #52
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    lucast2007us wrote: »
    Hey John looks good how can you tell me how much did your heat pump cost with labor costs etc?

    Nothing, because I don,t have one but there are lots of posts re installation & running costs on this thread.


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    #53
    Noodle Scratcher
    Registered Users Posts: 42 ✭Noodle Scratcher


    Maths? graphs? my head hurts now. I think I’ll stick with the boiler!


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