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657 posts

Ultimate Geek


#270651 20-May-2020 12:31
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So, our builder had prepared a slab for 2 x Panasonic heat pumps.
They ended up providing us with a different model, where one device outside can run both heat pumps in the house.
The slab is too big though, as the photo shows.
Is one large device cheaper to run, compared to two smaller?
Also, we’re still considering asking the builder to cut the concrete to fit the single device.
If we kept it, we would consider having some sort of storage right next to, but will the outdoor device require space around it (for air circulation)?
Still umming and arring, if we should have the slab cut to fit. Looks a bit weird with the much larger slab, I think.







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  #2487106 20-May-2020 12:54
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Length of concrete slab looks fine. You have even amount of space to stand either side of the compressor/condenser unit. It is quite normal now for a single condenser unit to be able to control multiple internal hi wall ac units. If you try and cut that concrete now, the remaining concrete underneath and around the condenser unit will develop cracks straight away. You can always lay a a concrete path around that side of the house with same colour concrete as what you have either now or later. 





Do whatever you want to do man.

  

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Ultimate Geek

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  #2487107 20-May-2020 13:04
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Recommended clearances on the back and (non service) side are quite small (150mm, but a larger clearance is recommended in front of the unit)

 

See page 23 here: https://consumer-nz-assets.s3.amazonaws.com/assets/2065/Good_practice_heat_pump_installation.pdf

 

 

 

Would need to dig into COP / EER ratings to compare the running costs of a multi-room system vs individual units.

 

 

 

Note that a 7kW (heating) unit is fairly small to be running multiple indoor units. We have an 8kW individual unit for our lounge. The sizing of your unit may be fine if your house is smaller and/or well insulated.

 

Main downside of multi-split units is that one unit can-not be heating while another is cooling.


 
 
 
 


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Uber Geek


  #2487113 20-May-2020 13:18
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I wouldn't cut the concrete, but that's just me. Risk of splitting etc and looking worse than it being big.

 

As to the unit, I guess it depends. We had the choice, and went with 2 external units, though ours is Toshiba not Panasonic. In our case, the single outdoor unit we were looking at would be running even if we had only 1 internal unit running, and thus be inefficient cost-wise. Split with 2 (1 to cover the living zones 1 to cover bedroom zones), it was more cost effective. But this was a couple years ago, and different brand, so they may be more 'smart' now.

 

 




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Ultimate Geek


  #2487121 20-May-2020 13:27
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billgates:

Length of concrete slab looks fine. You have even amount of space to stand either side of the compressor/condenser unit. It is quite normal now for a single condenser unit to be able to control multiple internal hi wall ac units. If you try and cut that concrete now, the remaining concrete underneath and around the condenser unit will develop cracks straight away. You can always lay a a concrete path around that side of the house with same colour concrete as what you have either now or later. 


Thanks. We’re planning on having artificial grass running up to the slab.
OK, will not ask them to cut the concrete smaller. I appreciate the input.



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Ultimate Geek


  #2487127 20-May-2020 13:33
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Scott3:

Recommended clearances on the back and (non service) side are quite small (150mm, but a larger clearance is recommended in front of the unit)


See page 23 here: https://consumer-nz-assets.s3.amazonaws.com/assets/2065/Good_practice_heat_pump_installation.pdf


 


Would need to dig into COP / EER ratings to compare the running costs of a multi-room system vs individual units.


 


Note that a 7kW (heating) unit is fairly small to be running multiple indoor units. We have an 8kW individual unit for our lounge. The sizing of your unit may be fine if your house is smaller and/or well insulated.


Main downside of multi-split units is that one unit can be heating while another is cooling.


I expect the 7kW to cover our needs. It’s only a 146m2 house, so certainly not massive.
You wrote the downside of the multi-split unit is that one can heat while another can cool. I see that as a good thing. Or did you mean that it can’t do both at the same time?

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  #2487131 20-May-2020 13:38
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a multi split can either heat on both units or cool on both units, not heat and cool.


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Ultimate Geek

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  #2487136 20-May-2020 13:47
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danepak:

 

I expect the 7kW to cover our needs. It’s only a 146m2 house, so certainly not massive.
You wrote the downside of the multi-split unit is that one can heat while another can cool. I see that as a good thing. Or did you mean that it can’t do both at the same time?

 

Yip. I have edited my post, sorry for the error.

 

Individual units can behave individually. But with a multi-split it is not possible to say cool the lounge while heating the bedroom. Admittedly a rare use case.


 
 
 
 




657 posts

Ultimate Geek


  #2487139 20-May-2020 13:51
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Scott3:

danepak:


I expect the 7kW to cover our needs. It’s only a 146m2 house, so certainly not massive.
You wrote the downside of the multi-split unit is that one can heat while another can cool. I see that as a good thing. Or did you mean that it can’t do both at the same time?


Yip. I have edited my post, sorry for the error.


Individual units can behave individually. But with a multi-split it is not possible to say cool the lounge while heating the bedroom. Admittedly a rare use case.


Thanks. I agree, probably won’t happen often (if ever).

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Master Geek


  #2487142 20-May-2020 13:53
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Not sure under what circumstances you'd want cooling and heating in different areas. I'd just just put a pot plant either side of the heatpump and call it done. It looks tidy as is. Airflow is a good thing for the units.



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Ultimate Geek


  #2487144 20-May-2020 13:55
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Froglotion: Not sure under what circumstances you'd want cooling and heating in different areas. I'd just just put a pot plant either side of the heatpump and call it done. It looks tidy as is. Airflow is a good thing for the units.

Yep, considered the plant thing too.

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  #2487146 20-May-2020 13:59
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In autumn / spring we occasionally use cooling in our kitchen which gets HEAPS of sun and heating in the rest of the house, but it's rare. Two smaller units probably a touch more efficient, but personally I'd go for whole house ducted heating. I really want to retrofit but my wife doesn't think it's worth the $12K - $15K, compared with two smaller heat pumps $8K plus oil heaters in the bedrooms in winter.




657 posts

Ultimate Geek


  #2487147 20-May-2020 14:02
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timmmay:

In autumn / spring we occasionally use cooling in our kitchen which gets HEAPS of sun and heating in the rest of the house, but it's rare. Two smaller units probably a touch more efficient, but personally I'd go for whole house ducted heating. I really want to retrofit but my wife doesn't think it's worth the $12K - $15K, compared with two smaller heat pumps $8K plus oil heaters in the bedrooms in winter.


One heat pump is in the livingroom. The other one is upstairs in the master bedroom.
We’ve got good insulation incl mid floor and also double glazed windows.

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  #2487153 20-May-2020 14:14
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My older house has retrofitted good insulation, double glazing, but nowhere near as efficient as a new house I expect. We have about 10kw high wall for the lounge and bedrooms, 7kw for the kitchen / dining area. The 10kw is a bit big, it turns on and off quiet regularly, I'd rather it stayed on and just went quieter as it's less distracting. It's good when it's really cold though.


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Uber Geek


  #2487158 20-May-2020 14:24
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timmmay:

 

In autumn / spring we occasionally use cooling in our kitchen which gets HEAPS of sun and heating in the rest of the house, but it's rare. Two smaller units probably a touch more efficient, but personally I'd go for whole house ducted heating. I really want to retrofit but my wife doesn't think it's worth the $12K - $15K, compared with two smaller heat pumps $8K plus oil heaters in the bedrooms in winter.

 

 

 

 

We got a ducted system retrofitted into our 100 year old villa last winter, 2 storeys approx 150 sqm but with a 3 metre stud.  Cost around $10,000  Ours has floor mounts upstairs and wall mounts down stairs.  We couldn't get vents to the masters, but when we get rid of the tenant downstairs will be able to.

 

Love it.  Its an 11 kw Fujitsu.  No smarts but heats the house brilliantly.  House warms up very quickly despite the house having more gaps than a sieve (all of the joinery is original) and only having floor and ceiling insulation. .    





64 posts

Master Geek


  #2487175 20-May-2020 14:49
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Froglotion: Not sure under what circumstances you'd want cooling and heating in different areas.

 

For what it's worth, and I'm sure this is a very specific case - we have a home gym which we use the heatpump in there for cooling while the lounge or bedroom ones can be heating.  But yeah outside of that probably very rare or unlikely it would ever be needed.


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