Facilitator: Dr Angus Gentle works in the School of Physics and Advanced Materials at UTS. He’s designing systems that may one day replace expensive air conditioning and refrigeration. Angus Gentle, thank you for talking to me today. You’re looking at paints that can help with cooling. What are they?
Angus: So we’re looking at paints, coatings and systems that we can put on rooves of buildings so that we can generate coldness that we can then store [in] liquids or just pumping the air through the buildings so that we can cool buildings.
Facilitator: So would you say that they’re smart paints?
Angus: You could say smart paints. Most of our stuff, we would want to use it in more than just a paint. You’d have a whole system around it where you have a coating and heat exchanges.
Facilitator: Can you go in to a little bit more detail?
Angus: The cooling is based on radiative cooling or night sky cooling which is similar to your windscreen of a car that gets frost on it on a cold night when other surfaces don’t get the frost. So you’re pointing up at the sky, emitting out certain wavelengths which the sky doesn’t absorb and so because the sky doesn’t absorb those wavelengths it doesn’t get any heat back from them. So we’re optimising our surfaces so that we can pump as much heat out as possible without absorbing heat.
There are currently technologies out there where people pump water through buildings on the floor or on the roof to cool them down but they’re using air conditioners at night to cool the water. So we could improve those further by cooling the water radiatively.
Facilitator: So how does it apply? How would you put it on a surface for example?
Angus: So to put it on to a surface we’re using sputtering which is a vacuum deposition technique which is used commercially for coating glass for building, architectural ones. So if you’ve got coloured glasses or reflective coatings on glass for buildings they’re usually done by sputtering.
Facilitator: How cold can you make it?
Angus: We’re getting down to about 15 degrees below the lowest temperature of the night. So when it’s say 10 degrees, we’ll get to minus five degrees so we can create ice which we were doing. We were making ice on the surface of our thing earlier in the year.
Facilitator: That must have been a pretty exciting day. Tell me more about that?
Angus: We had these surfaces which had been up on the roof for a little while and these surfaces are dependent on how much moisture is in the atmosphere so that depends on how transparent the atmosphere is and how much heat you’d be getting back from it. It was a nice dry sort of time of the year and the ambient temperature was quite cool. So we thought these will be quite good times for measuring it and you’re measuring the temperature even at five o’clock in the afternoon, the samples were already at about one degree and we thought this will be a good night for getting this thing. As it went through zero degrees you could see the cooling of the surface slow down as an ice layer formed on the surface and then it continued to cool down below that.
Facilitator:It’s pretty exciting to think how this kind of paint could be used in our every day lives isn’t it?
Angus: Hopefully once these systems are produced and optimised we’ll be able to put them on to rooves of buildings so that we can collect coolness in to say a water solution and then pump it through the building to keep the building cool and avoid having to use air conditioners.
Facilitator: So what would this mean for something like air conditioning and how would this technology compare with it?
Angus: Our system would be, you’d have a large surface on the roof of your house which is a panel which is facing the sky. Just like solar panels you don’t want it shaded by trees or anything like that. Then it has a heat exchanger in the back of it where you’re pumping a fluid through it which is stored in a large tank which you’d probably put under the house or beside it so that it’s not getting sun on to it to heat it back up and then you’re pumping it through the building to cool it off.
Facilitator: So what level of interest have you got from industry?
Angus: As with most cool roof paints for keeping things cool during the day industry is always going to be interested because it will be ways to minimise the energy that’s used by buildings and so because of that then you’re not having to burn as much coal because you’re not having to use coal for producing air conditioning electricity.
Facilitator: Are there some challenges in attracting the attention of industry?
Angus: Currently the price of electricity is very cheap but that’s going to be going up and there’s a lot more awareness on green issues these days so people are starting to look at it even as we speak.
Facilitator: How do you go about your research?
Angus: Okay so essentially we start off by doing optical models to see what different coatings, how they would perform; what their spectral properties are in visible and thermal wavelengths. From those optical properties we then will put them in to a computer model which will say how well they’ll perform; so how much cooling power we’ll get out of it. If they look good we’ll then deposit them using the sputtering. After we’ve deposited a film we’ll then characterise it spectrally to make sure it actually performs the same as it was supposed to. Then we’ll put the samples outside on the roof and see how well they perform to how much cooling they’ll actually do.
Facilitator: What kind of technology do you use?
Angus: We use a FTIR which is a Fourier Transform InfraRed Spectrometer to measure the spectral reflectance of the samples so then we can see what wavelengths they absorb at and what wavelengths they reflect at. We’ll then measure the hemispherical emittance using [an Emissometer] as well as using a [UVV visible] spectrometer to measure the optical properties in the visible wavelengths so we can see how they’ll perform in the sun. We’ll also measure the thickness of them using a Stepro Flowmeter and then take the samples out on to the roof, put them in our test rig to measure the temperature they will get overnight, then compare them back to the models.
Facilitator: It’s obvious that you have to have a lot of attention to detail but what is it that attracted you to this kind of research?
Angus: I’ve always been interested in different green technologies and this one’s a quite interesting one which the idea’s been around for many years but hasn’t really been picked up and used so we’re trying to get it out there and make it work.
Facilitator: I imagine it will be a very good day for you when you see your research being applied in people’s homes and in our every day lives?
Angus: Yes, once it gets out on to homes it will be quite a good day.
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