About to buy a house , has gas space heating Rinnai Energysaver 8kW (20MJ hour) natural gas.
Reverse cycle 7kW aircon COP 3.3 efficiency day & night tariff.
My gut feeling the aircon is cheaper to run ??
open to ideas & suggestions ??
Reverse cycle aircon / gas heater,cheapest to run?
(13 posts) (8 voices)-
MrEGuy
MemberI cant quantify it but in general these days the A/C is cheaper to run. If the space heater was the only gas appliance and the daily connection fee was taken into consideration then the A/C would be miles cheaper. Gas will also get more and more expensive as coal power plants are shut down and are replaced by more flexible gas plants. The fact that Australia in now exporting massive amounts of gas that use to be sold on the domestic market does not help.
When using renewable energy the A/C is absolutely greener. Also consider that you can't get gas from a solar panel.
I personally recommend replacing gas appliances with efficient electric appliances when possible and disconnecting from the gas grid.
Posted Sunday 13 Nov 2016 @ 7:36:34 pm from IP # -
David
MemberMrEGuy said:
Also consider that you can't get gas from a solar panel.True but you can produce it (Bio-Gas) yourself, although it's generally not something that's typically done in built-up areas, but it can be done and it's "green" to do so #just saying.
Posted Monday 14 Nov 2016 @ 10:07:09 am from IP # -
cava
MemberMrEGuy said:
I personally recommend replacing gas appliances with efficient electric appliances when possible and disconnecting from the gas grid.
From an energy security perspective, gas supply does not tend to be interrupted. Electricity supply in contrast (where I live) can be problematic.
Posted Monday 14 Nov 2016 @ 11:10:25 am from IP # -
Aircons were designed for cooling.They take the hot air at ceiling level pass it throung the heat exchanger to cool it and blow it towards the floor. This is great for cooling .
When you try and use the same design to heat, you are fighting against physics. The RCAC split system takes hot air at ceiling level and passes it through the heatexchanger to heat it and blows it towards the floor. As hot air wants to rise this will heated air will make a gentle curve upwards towards the ceiling. This leaves you sitting in the cold air at floor level as this cold air cant rise to the heat exchanger because physics keeps it at floor level.
The only way to try and get this cold air to move is to really blow that hot air down and this gives you an uncomfortable draft to sit in. If you slow the fan speed to avoid the draft the heated air takes a short cuit directly to ceiling level.
I argue that aircons may have a good COP but lose that benefit in the way they work at trying to heat humans at floorlevel.
They are only ok for small rooms.
I suggest you use solar air heating to bring the base temperature of your home up to a more comfortable level. Those extra few degrees in temperature can make the difference between being cold and being reasonably comfortable where you can survive without turning on extra heat. If you find extra heat is required it will not be as much to bring that temperature up as your home is already preheated.
I have studied this and have designed a solrheating system that will do this. As I am the owner I cannot give you the web address but anyone interested can PM me for more details. I have a graph of temperatures taken this winter in a two bedroom unit in Armidale which clearly shows this increase in the base temperature of the building,Posted Wednesday 16 Nov 2016 @ 12:02:41 pm from IP # -
MrEGuy
MemberYeah the concept of solar air heating is great, but your argument is completely flawed.
You are trying to sat that RCAC are not that efficient because of stratification (hot air rising) but this effects all types of convection heating. Even a gas heater on the floor will have its warmth migrate to the ceiling. A RCAC pointing the heat at the floor will still have the heat migrate to the ceiling but it will get a chance to mix with the cold floor air first. Ceiling fans are recommended to be used with all kinds of space heating to help minimise the effects of the hot air rising. I have RCAC and Raked (Cathedral) ceilings and the ceiling fans I installed 12 months after the RCAC made the world of difference. Ceiling fans also consume little power and they make up for the power they consume by circulating the air so that the heated air doesn’t get away from you.
Yes solar air heating is good but its houses for courses as it is not the same as on demand space heating.Posted Wednesday 16 Nov 2016 @ 1:42:08 pm from IP # -
The problem, as I explained it, still exists with RCAC. The use of the ceiling fans are an add on to try and overcome the problem. The draft situation is still there also even if you have ceiling fans.
Yes I agree horses for courses.
Some people do not have sufficient roof space to install enough solar PV to run the RCAC as they do use a fair amount of power. My argument was about using RCAC as heating systems. You say in your text that after 12 months you had to install ceiling fans. Why? Because the RCAC did not work well enough for you. I think you have agreed with my argument. Yes I agree that solar air heating is not on demand heating but neither is "GREENER" RCAC.
I did say that it was a method of increasing the base temperature. Some days this increase is sufficient to not require extra heating and on other days it will require some onn demand heating but this will be less then if no solar heating existed.
In fact this solrheating is actually storeing energy in the mass of your building without the need for expencive batteries.Posted Wednesday 16 Nov 2016 @ 2:19:37 pm from IP # -
Greg C
MemberI don't have AC at home, but have had experience with them at work and holidays. We stayed in an 'eco' lodge in WA for a few days 2 months ago, it was cold and it had RCAC. It worked very well. 2 reasons, it was not oversized for the space and I set it up correctly, temp at 22 degrees and fan on auto. The other good thing is it was sited so you didn't sit under it or in its draft. After running for about 20 mins it got the space nicely warm all over.
Contrast this to my old workplace. A 7kw unit in a room 2m x 5m, put there because it used to be the server room. 4 people worked in the room. The draft was so bad, you could not have the thermostat set below 28 in winter, you would walk back in to the room into a wall of heat but any attempt to cut this excessive heat meant some workers froze. The unit was way to big and it was not possible to avoid the airflow in that small room.
I'd say one of the main issues with RCAC is installing a unit that is too big, this is what the industry recommends. In our passive solar house we may need some extra heat for 1 month in winter. I have found that a 2.4kW fan heater is sufficient and it runs at 50% duty cycle after a while. I know I would be in an argument with any installer to put in a system that small
Posted Wednesday 16 Nov 2016 @ 8:03:38 pm from IP # -
Benny
Memberfranks its a fairly simple calculation if you know your energy costs. Assume gas heater is 100% efficient if its unflued. So if gas costs 14c/unit (as here in WA) then heat cost is 14c/unit(kWh).
For the AC if elec cost is 26c/unit, then heat cost is 26/COP ie 26/3.3 = about 7c/kWh. If you pay for gas per MJ then 1kWh = 3.6MJ so multiply cost per MJ by 3.6 to get cost per kWh.
WE have used RCAC for years now for heating and we certainly direct the heat downwards but no way is it an "uncomfortable draft". Whole room warms up nicely.
I'm surprised your solrheating works Con when the diagrams on your website also show that the heat is pumped back to the room through ceiling vents!Posted Saturday 19 Nov 2016 @ 12:22:36 pm from IP # -
johnmath
MemberThe cheapest type of air conditioning by a factor of several times is the one you don't need to use much. This type of low cost air condition is a byproduct of properly insulated and draft-proofed building construction with built-in passive heating and cooling, meaning AC is only used for a few hours on a few days of the year.
The $1000s saved annually in energy costs are a minor benefit compared to the joy of living in a house that is most often environmentally comfortable to be in without having to do anything, which is priceless. YMMV.
To answer con's concerns about drafts when heating with RCAC, just buy a Daikin and it's not an issue, nor will noise be for you or your neighbours. The Daikin will probably outlast the house, whilst the few $100s save buying a lessor brand will be forgotten in a couple of weeks.
Posted Thursday 24 Nov 2016 @ 12:48:51 pm from IP # -
Hello Benny
The reason for that is to fill the room with warm air, not blow it at the occupants. The warm air is drawn down by the fact that we actually remove the cold air at floor level this space has to be filled with warmer air.
I have been recording data of the temperature in a unit of 90 sq metres. I started the data recording one month before I installed the solrheating and the rise in the over all temperatures was dramatic. I have the graph on my solrheating facebook page. I have no idea how to place a graph in here. But it is an interesting graph to have a look at. You will notice that the night time temperatures are above what the daytime temperatures were before the system was installed,which means that the system is storeing the daytime energy in the building mass. So we have a method of storeing energy without the use of expensive batteries. and there will never be a need to replace this storage medium. This result was obtained with just one panel more panels would show a much better result as you can imagine. I have had the system tested at the university of new england and the forty page test report is available. I will be downloading it onto my website soon. if you are interested i could email you a copy.Posted Monday 28 Nov 2016 @ 1:39:20 pm from IP # -
Johnmath
You are so correct yes passive heating is by far the best. I have been designing and building passive houses here in cold Armidale since the 70's. Putting it simply my solrheating system is the lazy mans passive heating . By positioning the solar collector in the right spot you can suck up to 90.5% of available solar energy as is shown in the test report. I have done some rough calculations and worked out that one of my solrheating panel brings in the equivalent solar energy of a north faceing sliding glass door some eighteen metres long without the disadvantage of the heat loss through such an expansive area of glazeing. I am not so sure about the Daiken outlasting the house as there are many moveing parts in an RCAC system. Many parts mean many places for faults and the ned for expensive repairmen. The solrheating system has just the one moveing part, the inline ductfan that can be replaced by any handyman or homeownerPosted Monday 28 Nov 2016 @ 1:53:43 pm from IP #
