People tend to view ceiling height as purely an architectural choice, but it can also have a very real impact on the performance of ducted heating & cooling systems. In Australia, which is a bit of a hot spot when it comes to heating & cooling, the numbers are pretty telling. Heating and cooling can account for anywhere from 20% to 50% of a household’s total energy consumption, depending on where you live. And with many newer homes opting for higher ceilings of 2.55m, 2.7m and even 3m, the volume of air that needs heating or cooling increases significantly. Research shows that ceiling height can influence not just the amount of thermal demand, but also airflow distribution, temperature stratification and just how big a heater or aircon you need. This makes it a pretty important factor when it comes to overall HVAC performance and operating costs.
Higher Ceilings Raise the Volume of Air that Needs to be Conditioned
The most obvious impact of higher ceilings is that the amount of air inside a room goes up. Take a standard 50sqm room with a 2.4m ceiling. That’s 120 cubic metres of air. But raise that ceiling to 3m and all of a sudden you’re talking about 150 cubic metres. A 25% increase in air volume. This means a lot more air that needs to be heated or cooled. And that adds a load to your heating and cooling systems.
For homeowners who need ducted heating and cooling Melbourne, ceiling height is something that can have a noticeable impact on annual energy consumption. We found that by using the parameters set out in the Australian National Construction Code, increasing the ceiling height from 2.4m to 3m in Melbourne’s climate zone resulted in about a 12% increase in annual heating and cooling demand. It was worth noting that the impact was much more pronounced in cooler regions where heating is the main load for a lot of the year.
Temperature Stratification: The Enemy of Efficient Heating
Warm air likes to rise, and in homes with high ceilings the warmer air ends up accumulating near the ceiling while the cooler air stays down at floor level. This is known as temperature stratification.
Cooling Systems Are Less Sensitive but Still Pay the Price
Cooling systems tend to do a bit better than heating systems when it comes to ceiling height. Cool air tends to sink rather than rise. But while that might make cooling systems less sensitive to the impacts of high ceilings, it doesn’t mean they’re completely immune.
Air Distribution Challenges Start to Get a Whole Lot More Complicated
Ceiling height makes a big difference in how the conditioned air moves around a space. The higher the ceiling the worse it gets. Typical standard residential diffusers only work well with ceilings between 2.4 & 2.7 metres. As soon as you go above that, airflow patterns change. It’s even harder for that conditioned air to actually reach the people occupying the space.
The science guys who have looked into this have found that if you drop the supply air down from a high-ish point it really helps with getting indoor temperatures nice and even. It gets even trickier when you’ve got really high ceilings because you need a lot more air to cover the distance. You can end up with dead spots or uneven currents of air.
If you stick the diffusers in the wrong spot in these tall rooms it can lead to hotspots, cold spots, all sorts of issues that make people feel really uncomfortable even when the overall room temp seems fine. This makes duct layout and picking the right diffusers even more important the higher the ceilings get.
Higher Ceilings Can Let Heat In
It’s not just the extra air that you’ve got moving around. Taller ceilings give you more wall surface area to lose heat in the winter and pick up heat in the summer.
By way of example, bumping up wall height from 2.4m to 3m on a standard floor plan gives you an extra 25% surface area. That’s just begging to be let in or let out heat. And that extra “envelope” of the building (walls etc) lets through way more of those outside conditions too. Heating & cooling bills will go up. You can see it a bit more in the homes that don’t have very good insulation or a lot of glass.
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