Browse Forums General Discussion Re: R 1.0 or R 1.5 Reverse Cycle Air conditioning ducts 2Aug 10, 2016 6:35 pm I'd go with the R1.5 on the principle of efficiency. Whether it's economically rational or not might come down to the specifics, like the roof temperature of that house, and the amount of usage. Here are some numbers that you might be able to adapt: Some possible assumptions for summer usage: * Average roof space temperature on days when cooling: 45 degrees * Duct temperature: 18 * Duct surface area: 50m2 * Hours run per year: 10*50 = 500 Power loss for R1.0 = (45-18)*50/1 = 1350W Power loss for R1.5 = (45-18)*50/1.5 = 900W So it saves 450W of heat loading. If the EER of the A/C is 3, then that means 150W of electrical power. At $0.30/kWh supply charge, that's 150/1000*0.3*500 = $22.50 per year difference. At that rate the $400 has a 20 year payback. However, the numbers can look quite different. A dark coloured roof can get those roof temperatures up over 60 degrees on hot days. Also, if you use it for heating it winter, you might double the figures. Then if you use it for more than that 50 days per season, or 10 hours a day, it goes up as well. That could easily get you down to under 5 years payback. Another factor is the capacity. For cooling, the A/C needs to be sized for the hottest days. With a dark coloured roof, and 45 degrees outside, the roof is likely getting up towards 70 degrees. This alters the figures to: Power loss for R1.0 = (70-18)*50/1 = 2600W Power loss for R1.5 = (70-18)*50/1.5 = 1733W Given that the a/c is running in the de-rated region at those temperatures anyhow, taking that 1kW of load off, could see you drop back to a smaller unit - which might save your $400 back again. Otherwise, even with the larger unit, you might value the extra cooling you get on those hottest days. Re: R 1.0 or R 1.5 Reverse Cycle Air conditioning ducts 3Aug 10, 2016 6:57 pm oneJohn I'd go with the R1.5 on the principle of efficiency. Whether it's economically rational or not might come down to the specifics, like the roof temperature of that house, and the amount of usage. Here are some numbers that you might be able to adapt: Some possible assumptions for summer usage: * Average roof space temperature on days when cooling: 45 degrees * Duct temperature: 18 * Duct surface area: 50m2 * Hours run per year: 10*50 = 500 Power loss for R1.0 = (45-18)*50/1 = 1350W Power loss for R1.5 = (45-18)*50/1.5 = 900W So it saves 450W of heat loading. If the EER of the A/C is 3, then that means 150W of electrical power. At $0.30/kWh supply charge, that's 150/1000*0.3*500 = $22.50 per year difference. At that rate the $400 has a 20 year payback. However, the numbers can look quite different. A dark coloured roof can get those roof temperatures up over 60 degrees on hot days. Also, if you use it for heating it winter, you might double the figures. Then if you use it for more than that 50 days per season, or 10 hours a day, it goes up as well. That could easily get you down to under 5 years payback. Another factor is the capacity. For cooling, the A/C needs to be sized for the hottest days. With a dark coloured roof, and 45 degrees outside, the roof is likely getting up towards 70 degrees. This alters the figures to: Power loss for R1.0 = (70-18)*50/1 = 2600W Power loss for R1.5 = (70-18)*50/1.5 = 1733W Given that the a/c is running in the de-rated region at those temperatures anyhow, taking that 1kW of load off, could see you drop back to a smaller unit - which might save your $400 back again. Otherwise, even with the larger unit, you might value the extra cooling you get on those hottest days. Is this with Mac jones??? We didn't sign unless we were given permission to add another AC to our bronte build.. Anybody know any good and reasonably priced Air conditioning contractors/companies that could install a ducted air conditioning system in the Central Coast NSW for a small… 0 3243 How do you remove one of these ceiling air con vents? And is it possible to disconnect the duct joined to the vent from inside the house, without going into the roof cavity? 0 4038 Hi all, sorting out the ducted air con for a 350sqm double story house. Does this placement sound reasonable to you? Also, I plan to have 6 zones I think. Living room… 0 0 |