# Forum Home Renovation Heating & Cooling  Split system air conditioner questions

## ErrolFlynn

Im thinking of a split system cooling only air conditioner. Dont need heating as Ive got a gas room heater. 
I have a few questions: 
1. I read somewhere that you shouldnt have the wall unit near an open flame. They went on to say that its not because the refrigerant leaks, because it probably wont leak, but if it does, it will let out toxic fumes if it comes into contact with the flame. So, dont install it above your gas stove. But I was thinking of installing the wall unit above my gas space heater. I figure thats okay because you wouldnt have both running at the same time. Any thoughts? 
2. I suppose the shortest distance between the wall unit and condenser would be desirable. I was thinking of having the wall unit on one wall and the condenser around the corner of the house and on another wall. How good are the pipes at getting around corners, and what would the max length between units be that maintains optimum efficiency? Im thinking of loss in the pipes. 
3. I have gas cylinders for my gas heater. Is there a risk of fire by locating the condenser unit on the same exterior wall as the gas cylinders? 
4. I also read somewhere that the air conditioner should be run on its own fuse. That seemed like a big ask. Is that really necessary? How much current to do these things use? 
5. Most often the condenser sits on the ground, or bolted half way up the wall on a bracket.  Is it asking for problems to put them on the roof (flat tin roof), or is that a problem with the sun's heat and rain and weather beating on them?

----------


## GraemeCook

Good Morning ErrolFlynn 
There is nil to quite small variances in the cost of reverse cycle heat/cool air conditioners as opposed to cool only ones.   You could get more flexibility and cheaper operating costs. 
In Canberra electricity costs about 20 cents per kilowat hour and most heat pumps are 300% efficient, or more so that it costs about 6.7cents to put one kilowat of heat into your room.   [ 20 / 3 = 6.667. ]
Town gas costs about 2.5 cents per megajoule, equivalent to 9 cents per kilowat hour, and most gas flued heaters are about 80% efficient.  This means it costs about 11.25 cents to put one kilowat of heat into your room.  [ 2.5 * 3.6 = 9.0]  { 9.0 / 0.8 = 11.25 }
LPG is much more expensive than town gas, and unflued heaters are much less efficient - do not know if yours is flued. 
Re Question 5;  outdoor unit should be in a position where it can be easily serviced.  B-i-L in Melbourne mounted his just under the eaves so that he could drive car underneath it.  Seemed a good idea at time.  Rules changed;  now it is illegal to service it without erecting scaffolding = expensive. 
Other questions probably relate to ANZ Standards so I will leave to professionals to answer. 
Fair Winds 
Graeme

----------


## Random Username

...but in cold winter climates (ie Canberra) trying to heat with air conditioning is horrible...there's just not enough heat in the outside air to pump heat from! (not to mention the efficiency drops off once the outside air gets below a certain temperature) 
Current wise, yes, a separate circuit is a really good idea unless you like resetting the circuit breaker with regularity.  Check the specifications of your unit and see how much power it pulls.

----------


## krico

> Im thinking of a split system cooling only air conditioner. Dont need heating as Ive got a gas room heater. 
> I have a few questions: 
> 1. I read somewhere that you shouldnt have the wall unit near an open flame. They went on to say that its not because the refrigerant leaks, because it probably wont leak, but if it does, it will let out toxic fumes if it comes into contact with the flame. So, dont install it above your gas stove. But I was thinking of installing the wall unit above my gas space heater. I figure thats okay because you wouldnt have both running at the same time. Any thoughts? 
> 2. I suppose the shortest distance between the wall unit and condenser would be desirable. I was thinking of having the wall unit on one wall and the condenser around the corner of the house and on another wall. How good are the pipes at getting around corners, and what would the max length between units be that maintains optimum efficiency? Im thinking of loss in the pipes. 
> 3. I have gas cylinders for my gas heater. Is there a risk of fire by locating the condenser unit on the same exterior wall as the gas cylinders? 
> 4. I also read somewhere that the air conditioner should be run on its own fuse. That seemed like a big ask. Is that really necessary? How much current to do these things use? 
> 5. Most often the condenser sits on the ground, or bolted half way up the wall on a bracket.  Is it asking for problems to put them on the roof (flat tin roof), or is that a problem with the sun's heat and rain and weather beating on them?

  1: Not a problem with this. If installed correctly and tested for leaks.  
2: All units come precharged for certain distances depending on brand. What sort of distance are you talking. You can always add gas if your pipe run is longer than the precharged length. There are maximum runs too depending on pipe size. Plus your pipes can go through the roof space too to cut down on length.  
3: No 
4: Safer to have a separate circuit. Current will depend on size.  
5: I have put plenty on roofs and not an issue, depending on location. Would not advise putting it in direct western sun though.  
Krico

----------


## Smurf

Whilst they aren't great when it's zero or below outside, reverse cycle air-conditioners certainly do produce heat very cheaply compared to bottled gas or other electric heaters. And they certainly work when it's cold but not ridiculously so. 
I'd get a reverse cycle model, the cost of which will be only slightly higher than a cooling-only unit anyway. Even if you only use it to supplement the gas heating, you'll save money. And given that it shouldn't cost much more to buy anyway, why not get reverse cycle? With that plus keeping the gas, you'll have the best of both. 
Some years ago I purchased a reverse cycle system for my mother's house to replace a bottled gas heater. The sole reason was to save money, noting that she is now 70 and spends a lot of time at home. The money saved on heating costs since then has paid for the cost of the system several times over (literally). 
Gas heating is "nicer" certainly, but reverse cycle A/C is heaps cheaper to run and more than good enough when it's cool enough to need heating, but not to the point that it's snowing.

----------


## ErrolFlynn

Thank you for the responses.  Brilliant feedback. 
I must say Im shocked, dismayed, and confused.  The property is located on NSW south coast.  It gets cold but not icy like Canberra. 
I havent bought anything as yet.  Just contemplating it.  I was thinking of cooling only because I have just bought a gas room heater.  The kitchen stove blew up and I have just bought a new fully gas cooker.  I went for gas because I figure it would be cheaper to run than an eclectic cooker.  I had to get gas cylinders.  Elec costs are going up.  I figure cut the elec heaters and get a gas space heater at the same  time.  Ive got both cooker and heater in the house, but not yet installed. Just waiting for the gas man.  Anyway, gas is easier to cook with. 
Im going to put the place up for rent on the stayz site when everything is done.  I was thinking an air conditioner would probably be nice for the punters.  They probably expect it in summer.  So, for those cooler nights I figure it would be cheaper to put the gas (flued) heater on than have someone flick the air conditioner on to the heating cycle. (This is my shocked and dismayed bit, because Ive already bought the stuff.) 
And my confusion.  How can a reverse cycle air conditioner be 300% efficient?  Please respond in simple terms.  I understand that old reverse cycles used a heating element inside, as your average elec radiator does.   And that newer designs use heat pump technology.  I must admit I had only heard of heat pumps involving miles of piping buried deep in the garden that are used to suck out retained heat from the soil.  However, I have trouble understanding how a decent amount of heat can be drawn from cold external air and used to warm a house.  I have trouble understanding how such a unit could be economical to run.  Ive read stuff on wiki about air conditioning come heat pumps, which I could appreciate was an improvement on the old design, but never considered that it would be much better than to raise the temperature by a few degrees more than outside air temp.  Just showing my ignorance here.  If you said 30% efficient Id have thought that was impressive. 
The wall Id like the wall unit on is west and is the same one the gas cylinders are located.  I was worried about sparks.  Placing the condenser unit on the south wall would involve about 4 metres horizontal travel for the pipes and maybe another 1 or 2 metres on the south wall, and then as the wall unit is on the 1st floor and the condenser would be on the ground there would be a vertical travel of about 5 meters, I guess.  So that would be about 11 metres all up.  Thats why I was thinking about a roof installation, but there is no shade up there.

----------


## Smurf

A reverse cycle A/C does not "create" heat as such, it simply moves (or "pumps") it from one place to another. In Tasmania they are universally known as "heat pumps" for that very reason and about 40% of homes in Tas are heated this way. 
In layman's terms, you have electricity being used to power the compressor (main load) and fans (which use relatively little electricity). In heating mode, it's simply taking heat from outside and moving it to inside, the reverse of what it does in cooling mode. It's the same as your fridge - it doesn't "create" cold, it's simply taking heat from inside the fridge and moving it to outside - feel the back of the fridge and you'll find it's warm for this very reason. 
So, you have say a 1kW compressor, and it's going to put about 3kW of heat into the room (or about the same heat going outside. Most of that is heat absorbed from the outside atmosphere, plus a bit of heat from running the compressor motor itself. So you get 3kW, but are only using 1kW of electricity. Hence it's fairly cheap as a means of heating. Electricity itself may be more costly than gas, but in this case you're not using much of it relative to the amount of heat produced. 
A heat pump isn't 300% efficient in an engineering sense, but since you're only using 1kW in order to get 3kW of heat into the room, it can be considered "300% efficient" from a practical perspective. Pay for 1, get 3. You use a relatively small amount of electricity, to "concentrate" a larger amount of heat from the outside air and then bring it inside where you want it.  
There are no thermodynamic principles being broken here, since you are moving heat not creating it. The heat which magically appears is really just coming from the outside air - hence the cold air blowing from the outdoor unit when it's in heating mode (and vice versa when it's in cooling mode). 
All that said, reverse cycle A/C isn't the "ideal" means of heating in that it loses effectiveness when it's bitterly cold. But it's cheap and easy - hence their popularity in Tas where due to the climate heating is often a significant household expense and mains gas (which is cheaper than bottled gas) isn't widely available. 
All that said, there's nothing "wrong" with gas for heating and it's a "nicer" heat I think most would agree. I'm just saying that if you're going to get a split system, then getting a reverse cycle one makes sense.

----------


## GraemeCook

Good Morning ErrolFlynn 
Cannot really add much to Smurf's excellent explanation. 
Whilst heat pumps are less efficient when the outside temperature drops below 5ºC, they are still quite effective and efficient - efficiency drops to perhaps 200% at 0ºC.   Most complaints can be traced to undersized units.   In Tas heat pumps and wood heaters collectively warm around 90% of homes. 
They are also a dominant heating method in northern Europe - Scandinavia, Germany, etc, where the winters are far more rigorous than Aus and heating optimised heat pumps there now routinely exceed 400% efficiency.   European brands are rare on the Aus market. 
Fair Winds 
Graeme

----------


## Random Username

The biggest drawback from my point of view is that heat pumps are slooowwwww to warm rooms up.  Put the ducted gas on at 6am on a winter's morning when it's 15 degrees inside, and in a few minutes you have air at 20 odd degrees coming out the vents; put the r/c air con on, and in a few minutes you have air coming out at 15.1 degrees...five minutes later, it's 15.2...by the time you've made tea and had brekkie, it might be just pushing halfway to 16 degrees.   
I found it generally started to get warmer when I turned it off to leave for work....

----------


## GraemeCook

> The biggest drawback from my point of view is that heat pumps are slooowwwww to warm rooms up.  Put the ducted gas on at 6am on a winter's morning when it's 15 degrees inside, and in a few minutes you have air at 20 odd degrees coming out the vents; put the r/c air con on, and in a few minutes you have air coming out at 15.1 degrees...five minutes later, it's 15.2...by the time you've made tea and had brekkie, it might be just pushing halfway to 16 degrees.   
> I found it generally started to get warmer when I turned it off to leave for work....

  
Sounds like Random's got/had and undersized or improperly installed heat pump.

----------


## Random Username

Correctly sized, professionally installed, worked great on cooling....but Canberra's minus 6 mornings really didn't show it at its best!

----------


## Smurf

I don't doubt that gas will deliver a more effective blast of hot air on a morning when it's well below zero outside. 
But if you're going to install an A/C anyway for cooling, then it makes sense to get one that also heats. Even if you only use it for half your heating, you'll save on running costs compared to LPG or ordinary electric heaters.

----------

