Is heat pump COP based on average use? « Alternative Technology Assn Forums

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Is heat pump COP based on average use?

(12 posts) (7 voices)

Started 8 years ago by Boyd
Latest reply from Lance

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RC-3

Boyd
Member

We are looking at a Reverse cycle unit to heat our 68 square meter living area in coastal Sydney.
The following guide suggests a 5.6kW system: http://www.choice.com.au/reviews-and-tests/household/heating-and-cooling/home-cooling/your-cooling-options-buying-guide/page/cooling-calculator.aspx
It's a cooling calculator but assuming it works for heating as well. We don't need cooling. We have been improving our passive heating as much as possible.

I'm wonderring if the calculated COP is based on some kind of average use of the appliance?
Smaller units seem to have better COPs but installers we have had visit claim these would be "running too hard and wear out".
They recommend a 7.8kW 6.5kW(C) 8.1kW(H) rated unit with COP of 3.53
A smaller unit we've found that's 4.2kW(C) 6kW(H) has a COP of 4.44
Should we believe the installer or the online calculator?
Any advice most welcome.

Posted Saturday 8 Jun 2013 @ 8:40:07 am from IP #
TonyT
Member

Boyd

Links that may be useful:
http://www.ata.org.au/forums/topic/2919#post-24341
http://www.ata.org.au/forums/topic/7773#post-42898
http://www.ata.org.au/forums/topic/7773#post-43184
http://www.ata.org.au/forums/topic/7773#post-43729

Posted Sunday 9 Jun 2013 @ 7:06:55 am from IP #
Boyd
Member

Thanks Tony they are the threads I needed

Posted Tuesday 11 Jun 2013 @ 10:36:17 am from IP #
Greg C
Member

I would suggest even the smaller unit you have listed there would be excessive. If it can put out 6kW of heat that should heat the space very (too) quickly. Our house, open plan has about 80 square metres that can't be separated and so must be heated. If we need to boost the passive solar gain we use a 2.4kW fan heater. It is perfectly adequate, however we set the thermostat so room temp is kept at 20 degrees. We don't use the heater unless interior temp drops below 18. We were in Canberra over the weekend and the halls of the hotel were kept at 19 degrees, perfectly adequate.

Another trouble with heat pump systems that are too big is the air movement which either ups the wind chill factor or forces you to sit in the hot air exiting the unit. This is certain to have you reaching for the remote and turning the temp up continually. Also make sure you get a unit that stops completely when the set temp is reached. The unit in our Canberra hotel did not so non heated air was being circulated when the set temp was reached. We had to manually start and stop it, the other alternative would be to turn the thermostat up which goes against the grain.

Posted Tuesday 11 Jun 2013 @ 11:47:50 am from IP #
TonyT
Member

Greg C

Agree 100% !

The inverter technology that is used in the best modern reverse cycle air conditioners helps to reduce the air movement - but the chill-factor remains.

The key is to build with maximum insulation in order to minimise the required amount of heat input and hence to minimise the required amount of air movement.

With hydronic wall panels or with hydronic floor heating the air movement is imperceptible.

Posted Tuesday 11 Jun 2013 @ 9:36:38 pm from IP #
Boyd
Member

From forum posts it sounds like the factors that might produce a high COP are:
1. well matched internal and external (inverter) units (Mitsubishi Heavy for instance have different outside units for every inside one)
2. how it's used: find a unit with a good low heating capacity (.6-6.9 kW say) so it can be run slow over a longer period without cycling
3. find one that CAN be run slow and has low fan speed to reduce cold drafts. (the lowest I've found is 83 L/s)
4. try and keep room temperature at 18-20 deg
I'm thinking a floor unit that can blow out at floor level might be good as a wall unit must need to run the fan higher to get the air down.
Does this sound like I'm on the right track?

Posted Wednesday 12 Jun 2013 @ 12:33:13 am from IP #
yabbietol
Member

I was wondering about the functionality of the larger split systems with in ceiling cassettes they are at the larger end of domestic split systems and avoid the ugly looking wall mounted internal units. They also offer the potential for multiple ceiling mounted units from one larger outside unit. They also avoid the need for cleaning duct work that comes with ducted A/C and is often cause of health problems from mould and dust.
Mitsubishi seem to make a range of them how do people rate them?
Also I cannot seem to work out how efficient they are with various sized outside units?
http://www.mitsubishielectric.com.au/Mitsubishi_Cassette_Air_Conditioning.html

Posted Wednesday 12 Jun 2013 @ 3:53:16 am from IP #
Boyd
Member

Hi Greg and Tony, am about to get a unit Fujitsu AGTV14 current favourite partly because no one will instal the smaller one! I would value your opinion on my previous post.
Yabbietol- those ceiling units are pretty ugly to!

Posted Friday 14 Jun 2013 @ 1:03:34 am from IP #
yabbietol
Member

Beauty is in the eye of the beholder. Each to their own.
If you look at the ceiling units on the web you get different cops for each unit, so it appears the internal unit not the outside units determines efficiency. I thought the whole system inside and outside would determine efficiency and overall COP.
I am still confused?
Does any one have any experience with split systems with ceiling units?

Posted Friday 14 Jun 2013 @ 4:56:12 am from IP #
ghostgum
Member

yabbietol, to achieve a range of capacities, some manufacturers use the same outdoor unit with more than one indoor unit. So a 4kW and 5kW indoor unit might both be using the same outdoor unit. This results in different efficiencies for the two units.

Posted Friday 14 Jun 2013 @ 5:40:11 am from IP #
ptera
Member

Gday there! Can anyone point me to a forum that may be able to help me on a mini temperature data logger. I bougt two RC-3 loggers from China thru eBay recently. The written instructions were in English but the software was Chinese and won't run on either PC or Mac. This is a very common data logger used in refrigerated containers for export, so I guess someone must have an English version.

Many thanks,
Ptera

Posted Wednesday 19 Jun 2013 @ 5:10:11 am from IP #
Lance
Key Master

If the file was a rar file, that's a type of compressed archive, you need to uncompress it using something like winrar or 7 zip (http://sourceforge.net/projects/sevenzip/?source=dlp) or similar, then run the exe file. I found a rar file with an exe that works under win 7 64 bit at http://www.goodluckbuy.com/images/detailed_images2/file/RC-3.rar

Posted Wednesday 19 Jun 2013 @ 7:44:15 am from IP #

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