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Caernarfon 18kW ASHP review


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Our air source heat pump has been in operation for five months, over spring and summer, so it is a good time to review the performance and efficiency of our Caernarfon 18kW Eco Air Source Heat Pump (ASHP) from Global Energy Systems.

 

Most ASHP owners in the UK use Mitsubishi, Hitachi or Daiken ASHPs, so it should be interesting to see how a British manufactured ASHP, supposedly made for the British climate, will perform and compare.

 

As part of this video, I’ve addressed our coefficient of performance (COP), performance and efficiency, the control panel and settings for the ASHP, noise rating and some general thoughts.

 

As I am not an ASHP expert and still trying to learn, I look forward to receiving your feedback and comment. I always take all the feedback you guys at Buildhub have to offer on board, and find it extremely enlightening.

 

I will do a follow up video in autumn and winter to provide a full performance and efficiency comparison.

 

YouTube:

 

Additional information and data sheets: http://myhomefarm.co.uk/air-source-heat-pump-efficiency-and-performance-review

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8 minutes ago, SteamyTea said:

Going to be hard to gauge the effectiveness of any ASHP over the late spring and summer months.

Do you collect external weather data?

 

Totally agree - but I wanted a baseline (spring and summer) to gauge effectiveness over autumn and winter.

 

I only collect temperature - should I also be collecting humidity?

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You should at least know how much DHW energy us needed. 

Wind direction and speed have a big affect on performance.

Strong South Westerlies are warm, week Easterlies and Northern winds are cold, and in winter there is little solar gain to be had in the 6 or 7 hours of daylight.

 

Edited by SteamyTea
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  • 2 months later...

Possibly as the air may well have a high RH.  This may be causing some frosting up of the unit.

There is usually an 'odd' temperature where the CoP drops, this is often just above 0°C.  Below that, the amount of water that is actually in the air is lower (it has frozen out already).

This is why ASHP are oversized, they basically have a larger radiator that takes longer to frost up.

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So if RH is low, does this help the ashp’s efficiency?

 

Checked our panel - RH at 27% and the boiler hasn’t kicked in once to defrost. Didn’t realize there was a correlation between RH, ambient temperature and ashp CoP.

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Mine is 99.9%, but there is a proper storm on.

 

At 27% RH, you should not have a frosting problem, and the CoP should be reasonable.

Can you check that the supplementary heater is not coming on, that would make it use a lot more juice.

The other thing is that it is probably running constantly.

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7 minutes ago, Home Farm said:

Internal. 3C outside.

 

Roughly speaking, for constant absolute or specific humidity [¹],  the RH doubles for every 10 °C drop in temperature so if there's temperature difference of about 20 °C between indoors and outdoors the outside RH would be just about 100% if it's 27% indoors.

 

[¹] I forget which, it doesn't make much difference anyway.

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On 14/11/2019 at 16:10, SteamyTea said:

Mine is 99.9%, but there is a proper storm on.

 

At 27% RH, you should not have a frosting problem, and the CoP should be reasonable.

Can you check that the supplementary heater is not coming on, that would make it use a lot more juice.

The other thing is that it is probably running constantly.


Frosting has not been an issue today.

 

We are averaging 2.5kW/hour on our ashp. Average outdoor temperature has been 0-3C. Would that be considered as being high? It looks like that to me.

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22 minutes ago, epsilonGreedy said:

How big is Home Farm?

 

Also what internal temperature do you maintain?

We’re heating just over 4,000 sqft - it’s all heated 24/7. Minimum temperature throughout the house is 19C. UFH from 8:00-21:0O is set to 21C. Bedrooms to 21C at nighttime (20:30-8:00), TV room to 21C in the evening. All other dormant rooms are set to 19C.

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2 hours ago, SteamyTea said:

That is about 7W per square metre for the electricity.

So somewhere around 15 to 20 W per square metre thermally.

 

Just a bit higher than mine, and I am probably 5 deg warmer.


So you’re running at 24-25C? Is that right?

 

For our numbers, is that an acceptable figure?

 

Every time I feel like I’m getting more comfortable with ASHPs, something comes along and it all unravels.

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15 hours ago, SteamyTea said:

No, my external temperature is 5°C higher.

As you have an old place, that is quite large, I think 50 to 60 kWh/day when it is ~2°C outside is not that bad.

Your home is nearly 8 times larger than mine.

 
Thank you for the explanation. Never thought about heating in W per square meter. I think that’s a very good way for me to monitor our running costs.

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  • 3 weeks later...

I’ve been monitoring our New Mitsubishi ASHP over this last cold spell

 

in November we’ve averaged about 55kWh/day Usage and it’s been fairly cold, 0-5c mainly. 

 

Highest usage was 1st dec when the temp was -2 most of the day, with a max of 3c. 100kWh usage with 230kWh heat output.  Windy too

 

That day we ran at 50c but usually we’re around 45c

 

We’ve added a load of insulation on our vaulted.ceilings this year. The two rooms without take a lot longer to get up to temp so we’re going to have to just bite the bullet and pull down the freshly plastered ceiling to add some insulation there too. 

 

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Our air source heat pump has now been operational since the spring. It’s time to see how it performed over the course of the past three months as part of our autumn air source heat pump review.

 

To see how it performed over the autumn, including a very cold November, please check out this video.

 

 

 

Additional information and data available here: https://myhomefarm.co.uk/caernarfon-18kw-autumn-air-source-heat-pump-review

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@Home Farm interesting update

 

your house is configured very similarly to ours. Ours is also long and thin but our main aspects are North/South so every room has a North and a South wall. 
 

Our two rooms I discussed had a similar issue. We have big tads in there but they weren’t particularly warm

 

We know from having the walls replasterrd that the pipes drop down in 10/15mm which means they don’t support the flow rate necessary to provide the maximum heat output for the radiator at the lower temps. I wish we’d have replaced them then but it was pre ASHP

 

To work around this we closed off a lot of other radiators lock valves to just 1/4 turn. They continued to work the same as before. Then we closed the towel rads right down. Similar yours they were piping hot with no TRV. They are also piped in 15mm so hogging the heat

 

this helped a lot. However when the temp was <3c we did have to put the flow temp up to 50c for a couple of days. It might be worth you moving to weather compensation mode and set it between 40c and 50c

 

ultinatwly if there’s no enough heat output you need to either increase size of rad (no use if they aren’t fully hot), increase flow rate or increase temp. 
 

 

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