Central heating vs heat pumps.

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#1817196 9-Jul-2017 12:29

Technofreak:

Yes, this is a possibility.

I have based my expectations on the fact the heat pump we have installed uses 30% less power than the old heater and produces up to 2.5 times the amount of heat.

I suspect where people have experienced a much larger bill than expected is where the heat pump is spending a significant amount of time defrosting. Our unit has rarely needed to defrost. I think the other issue is the one mentalinc talks about in his/her post. That is the disparity between the temperature set on the controller and the actual room temperature.

In our case a temperature setting of 18 degrees gives about 23 degrees room temperature. That is because the temperature sensor is in the unit which is mounted on the floor. The temperature measurement is taken from the air being drawn into the heat pump and when the room temperature is 23 degrees the air temperature at floor level is 18 degrees.

In this case if you were purely setting the desired room temperature by reference to the setting on the controller you would be attempting to achieve a room temperature of around 28 degrees and as such wasting a lot of energy.

Heat loss increases with the area heated and the temperature difference. It'll be interesting to hear how it goes.

We find even with the high wall models it gets a bit hotter than we set. A setpoint of 21 gives 22 to 23 with our Fujitsu, but it takes a setpoint of 20 to get there with the Daikin.

jnimmo

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#1817197 9-Jul-2017 12:33

Got an 11kW Fujitsu ducted covering an area about 105m2 in Christchurch, have been impressed with how well it copes on the cold mornings so far (although haven't had a snow day)- and power bill isn't crazy.

Have it turn on at 6:00am for 1 hour to 16 degrees. Usually have a couple of the bedrooms dampered off though so isn't heating that whole area at once.

(Having said that, I just checked out the temperature graphs, and even when outside temp was -2 inside was 14.5 degrees, so it is only having to bring it up a couple of degrees)

Would never want to go back to not having a ducted!

jonathan18

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#1817205 9-Jul-2017 12:58

mentalinc:

Some friends have underfloor heating using water set to 35 degrees in 400+sqm house and use around $400 of deisel a month, so would not be recommending that route. they Might ned to do some fine tuning on their setup but far from economical.

I'd vote ducted heatpump so long as the temp sensors that drive it are installed appropriately.

We just had it done and control unit is set to 17 degrees but the rooms run around 22 degrees! much work required by installer to sort it out still.

A five degrees variation is huge! We have a similar issue with the sensor in our lounge, which measures it two degree cooler than it is, ie to have the house at 20 we need to set it to 18; the frustrating thing is the lowest is 16, so we can't maintain a lower temp (say when out) than 18.

We had them replace the sensor but it's no better. The sensor in the bedroom, though, seems pretty accurate.

The initial problem with the temp sensors we had, though, was enormous - the installers tried to make us rely on the return duct sensor only, so no reading in the main living area at all (no sensor in our controller) - that led to the stupid situation of the temperature in the house varying by five degrees (due to the sensor being at the height of the 3m ceiling!).

Ducted systems are complex, and my experience is that some installers don't understand the issues or how to design a system properly; sensor positioning is but just one of the issues...

Bobdn

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#1817207 9-Jul-2017 12:59

I'm tossing up between a new gas heater or gas central heating.

https://rinnai.co.nz/central-heating

If I go central heating I'll go with one of those Genesis bulk gas deals. maybe just the $99 plan. I have a small amount of shares in genesis from the IPO so always feel compelled to buy from them :) but I'm sure other providers probably offer similar all you can eat plans.

https://signup.genesisenergy.co.nz/gaspackages/

smalltrader

174 posts

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#1817288 9-Jul-2017 15:10

Bobdn:
I'm tossing up between a new gas heater or gas central heating.

https://rinnai.co.nz/central-heating

If I go central heating I'll go with one of those Genesis bulk gas deals. maybe just the $99 plan. I have a small amount of shares in genesis from the IPO so always feel compelled to buy from them :) but I'm sure other providers probably offer similar all you can eat plans.

https://signup.genesisenergy.co.nz/gaspackages/

Rinnai is great and proven for gas water heating. For gas central heating I would suggest a Brivis unit. Brivis had proven reliability history. Caveat is servicing every two years. No different to cars all machines need servicing. Gas central heating is great with no cold spots in the house.

Very economical if you combine gas central heating, gas not water and gas cooking,. I am talking abouts piped gas not bottled gas.

dolsen

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#1817369 9-Jul-2017 16:10

Bobdn:

If I go central heating I'll go with one of those Genesis bulk gas deals. maybe just the $99 plan. I have a small amount of shares in genesis from the IPO so always feel compelled to buy from them :) but I'm sure other providers probably offer similar all you can eat plans.

https://signup.genesisenergy.co.nz/gaspackages/

The last time I looked, in Wellington, the bulk gas deal was actually more expensive than using the esaver plan and, if you used less, you paid less. Make sure that you compare the cost vs the alternatives.

Bobdn

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#1817453 9-Jul-2017 19:40

dolsen:

Bobdn:

If I go central heating I'll go with one of those Genesis bulk gas deals. maybe just the $99 plan. I have a small amount of shares in genesis from the IPO so always feel compelled to buy from them :) but I'm sure other providers probably offer similar all you can eat plans.

https://signup.genesisenergy.co.nz/gaspackages/

The last time I looked, in Wellington, the bulk gas deal was actually more expensive than using the esaver plan and, if you used less, you paid less. Make sure that you compare the cost vs the alternatives.

Thanks, will check it out.

Smalltrader, looks like the Rinnai system uses the Brivis gear.

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mattwnz

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#1817455 9-Jul-2017 19:45

mentalinc:

Some friends have underfloor heating using water set to 35 degrees in 400+sqm house and use around $400 of deisel a month, so would not be recommending that route. they Might ned to do some fine tuning on their setup but far from economical.

I'd vote ducted heatpump so long as the temp sensors that drive it are installed appropriately.

We just had it done and control unit is set to 17 degrees but the rooms run around 22 degrees! much work required by installer to sort it out still.

I know of a house that is about that size, using diesel as well, and recall that it is around that price to heat it. Underfloor heating designers I have spoken to will say that it is about $15-20 per day for heating that sized slab.

froob

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#1817462 9-Jul-2017 19:56

We have an older Brivis ducted gas central heating unit at our place. Can't comment on efficiency or cost vs a heat pump, but it heats our house very effectively and doesn't break the bank. Putting aside the type of heater, I would highly recommend central heating. Having the whole house warm is just brilliant.

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smalltrader

174 posts

Master Geek

#1817469 9-Jul-2017 20:17

I have a newish Brivis central heating unit (2013 installation from memory), six star efficiency rating. House is around 195 sq metre. Ducting to every room, including the bathroom. Gas is also used for cooking and water heating. My winter gas bill is about $200 per month. This is cheaper and warmer than my old place which was heated by night storage heater. Gas central heating the way to go if you can swallow the initial capital cost and have easy access to piped gas.

Wash

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Master Geek

#1818973 10-Jul-2017 16:38

jonathan18:

mentalinc:

Some friends have underfloor heating using water set to 35 degrees in 400+sqm house and use around $400 of deisel a month, so would not be recommending that route. they Might ned to do some fine tuning on their setup but far from economical.

I'd vote ducted heatpump so long as the temp sensors that drive it are installed appropriately.

We just had it done and control unit is set to 17 degrees but the rooms run around 22 degrees! much work required by installer to sort it out still.

A five degrees variation is huge! We have a similar issue with the sensor in our lounge, which measures it two degree cooler than it is, ie to have the house at 20 we need to set it to 18; the frustrating thing is the lowest is 16, so we can't maintain a lower temp (say when out) than 18.

We had them replace the sensor but it's no better. The sensor in the bedroom, though, seems pretty accurate.

The initial problem with the temp sensors we had, though, was enormous - the installers tried to make us rely on the return duct sensor only, so no reading in the main living area at all (no sensor in our controller) - that led to the stupid situation of the temperature in the house varying by five degrees (due to the sensor being at the height of the 3m ceiling!).

Ducted systems are complex, and my experience is that some installers don't understand the issues or how to design a system properly; sensor positioning is but just one of the issues...

When we first had our ducted heatpump installed, we found we had to bully the system sometimes to get it to cool the house on sunny days in autumn. It took me a couple of weeks to figure out what was going on.

Basically, the Panasonic systems can either measure at the control panel, or on the inlet side of the heat exchanger. They seem to default to using the temperature in the heat exchanger which was fine as I figured that way, it would get a view of the average temperature of the house in general. What was happening was the house was warming up due to solar gain through the windows, but the system didn't realise that the temperature in the house was rising.

I expect it wasn't measuring very well because:

1. While the ducting is insulated, it is only R0.9 or something like that, so any air sitting in the ducting would cool down over time

2. The system was only spinning up the fan to draw air through every couple of minutes and not for very long (10 seconds tops), therefore not pulling enough air from the house to flush the ducting and get an accurate temperature reading

Switching to use the panel temperature fixed that problem instantly!

We can hear the inlet ducts but basically can't hear the outlets. That is just because there are twice as many outlets as inlets, so there is more airflow per duct on the inlet side. We can also hear the external unit sometimes, as it is under the house (under the living room and main bathroom... well away from the bedrooms) but it is just a low hum, so it has never been an issue.

Power consumption is up a bit on the 7kW high wall we used to have in the lounge, but we no longer have that unit working flat out trying to cool the living room while the rest of the house bakes. We now have a pretty even temperature (whether we heat or cool) across the entire house. So overall, we've found the ducted heatpump to be excellent.

Senecio

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#1818986 10-Jul-2017 17:10

On a related note.

We have a heat pump in our open plan kitchen/dinning/living room. This area has gabled ceilings that lead to a mezzanine area over the living room into the master bedroom. The temp differential between the floor of the living room and the mezzanine area is about 8*C (~16*C to ~24*C with the unit set to 20*C). What is the best way of distributing the heat more evenly vertically. Was thinking of installing a ceiling fan above the height of the heat pump within fairly close proximity to the wall where the heat pump is installed to push air down away from the mezzanine to the other end of the open plan area where the kitchen is. Would this work? I do have a spare pedestal fan, I guess I could put that up on the mezzanine level to trial although it won't move anywhere near as much air as a ceiling fan.

RunningMan

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#1818988 10-Jul-2017 17:14

Wash:[snip]

Switching to use the panel temperature fixed that problem instantly!

+1 for this on the Panasonic ducted units - much more stable temp when measured in the area it is supplying, rather than at the indoor unit itself.

mentalinc

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#1819128 10-Jul-2017 19:44

I found that using the panel temp the rooms would spike in temperature varying by 2 degrees before heating up again which is not ideal.

also found the panel temp setting (ie set to 25 degrees overnight) and the rooms would swing between 20-22 degrees!

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Aredwood

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#1819248 10-Jul-2017 22:43

mentalinc:

I found that using the panel temp the rooms would spike in temperature varying by 2 degrees before heating up again which is not ideal.

also found the panel temp setting (ie set to 25 degrees overnight) and the rooms would swing between 20-22 degrees!

Where is the control panel located? If it is in the hallway then that is the problem.

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