Browse Forums Heating, Cooling & Insulation Re: How to size ac's for 6 star homes? 2Feb 15, 2011 3:16 pm The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: How to size ac's for 6 star homes? 5May 23, 2011 10:53 pm For our house they had to run it through the software and make some minor modifications to achieve the six star, mainly double glazing to the upstairs living areas of both houses. The a/c people have quoted for a 7.1kw split system to do the main room upstairs, what i'm struggling with is the fact that this room will be about 70sqm with really good insulation, double glazed windows etc yet at home have a 100sqm room, with large open stairwell, triple the glazing area with 5m raked ceilings topped with skylights...in 1980's construction methods, so not brilliant insulation, poor thermal efficiency glass etc...and yet its cooled and heated comfortably by a single 8.1kw split unit... Re: How to size ac's for 6 star homes? 6May 26, 2011 10:15 pm To accurately determine the heat load of such a place would really require a full extraneous heat load - not just a generic calculation. In relation to a 6 star rating the best you can do is find the most efficient A/C in the capacity required according to a "full extraneous heat load calculation" The higher the EER / COP rating (Energy Efficiency Rating / Co-Efficient of Performance) on both heating and cooling the more efficient the unit is. To determine the 6 star rating the whole home really needs to be audited - you will never find a 6 star A/C beyond maybe 2.0 - 2.5kW. Your builder should be able to run this report. Good luck You get what you pay for! Re: How to size ac's for 6 star homes? 7Jun 12, 2011 7:23 pm It is also difficult to do proper calculations because occupant behaviours often dictate what size unit is required e.g. thermostat setting, no. of hours heating/cooling during the day, whether they open curtains to let the sun in or open windows to let the breeze in. 50% of costs is related to this. Re: How to size ac's for 6 star homes? 8Jun 15, 2011 1:17 am IMHO....... Get a big one !!! With the technologies they have today "bigger" ones do not need to run at full power unless they need to run "at full power". In my experience (three ducted systems, numerous splits) the sales dudes UNDER quote, IMHO to get the lowest price and hence the job. We had one quote (I'm the dude who DOES read the fine print) where it actually said that "This system may not perform satisfactorily on days of extreme weather conditions". HELLO.... That's when I want it to perform, and perform darn well !!! My current philosophy is to get the "average" system recommendation and then get the next size up YMMV !!! P_D . Block settled 07 June 2011 Our little piece of the Interwebs on HomeOne....... viewtopic.php?f=31&t=48577&start=0 Re: How to size ac's for 6 star homes? 9Jun 15, 2011 9:39 am We have a passive solar design with R 3.5 ceiling insulation R 2.5 wall, reflective foil in all and double glazing. Winter temps get down to around 2-5 degrees. We have a Daikin Inverter AC that was sized to the standard 0.15KW/m2. We tend to zone at the most half of the house. Within 30min the thermostat setting is reached and then 60-90 min later the AC will turn off because the inverter has reached the lower limit for operation. In other words, it begins working like a switching non-inverter. Clearly the AC is oversized for our application. If you compare COP charts from the Daikin range non-inverters use about 10% more energy than inverters. Actron is the only manufacturer I know which can run at really low outputs. Re: How to size ac's for 6 star homes? 10Jun 18, 2011 7:50 am dymonite69 Within 30min the thermostat setting is reached and then 60-90 min later the AC will turn off because the inverter has reached the lower limit for operation. In other words, it begins working like a switching non-inverter. Clearly the AC is oversized for our application. We have two Daikin inverters in our house, and they both drop to low levels, and then turn on and off. Neither of them is oversized, as this happens even if it's very cold outside and they have to work hard when they turn on again. I think it's a change in the way Daikin build inverters now so they don't run down to really low settings. I think it may have to do with people feeling a draft when they are only going slowly, so not very much heat comes out. Because of this we are going to panel heaters for the current build. No drafts, no noise. My only worry is they won't heat the rooms up fast enough from a cold start, but we'll just have to see. Charlie Re: How to size ac's for 6 star homes? 11Jun 18, 2011 5:49 pm Charliektm400exc dymonite69 Neither of them is oversized, as this happens even if it's very cold outside and they have to work hard when they turn on again. Sizing is based on the steady state heat loss of the building when it has reached the target temperature. It isn't related to how quickly it takes to be heated up from cold. Re: How to size ac's for 6 star homes? 12Jun 19, 2011 6:44 am dymonite69 Charliektm400exc dymonite69 Neither of them is oversized, as this happens even if it's very cold outside and they have to work hard when they turn on again. Sizing is based on the steady state heat loss of the building when it has reached the target temperature. It isn't related to how quickly it takes to be heated up from cold. I don't think I was clear enough then. What I meant was when they turn on again as in turning on and off by themselves to maintain the temperature. Not bringing the temperature up from cold. Re: How to size ac's for 6 star homes? 14Jun 24, 2011 9:19 pm The house is having R4.1 in the ceiling and R3.0 in the walls...not sure if its getting foil though...the builder is higher end so expect it will have foil. Decided to go with the 7.1 KW system upstairs for the moment, they've recommended Daikin, i know they're suppose to be good but they don't seem to have all the features on the indoor head unit the panasonics/mitsubishi's have...have two split mitsubishi's over ten years old with no problems so i'm assuming reliability with these things isn't really a problem. There are two rooms on two levels to be air-conditioned, seen that Mitsubishi make systems capable of having multiple heads put on, are these very good? Or better off with two completely separate systems... The house will only really be used for maybe 4 weeks of the year but that usually includes some of the hotter periods just after christmas or again when Adelaide has a heat wave...that and the opposite in middle of winter...so the true extremes really... 10 years ago was a different software than we use now. it has had a lot of changes over the past years. 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