In recent years, like many Australian families we’ve been endeavouring to wean ourselves off fossil fuels.
There is no shortage of advice on the web on how to do this. The energy pundits all seem to be saying more or less the same thing: insulate the house; install solar PV; install heat pumps; turn off the gas; buy an EV. When we started out on our road to fossil fuel freedom I envisaged that we would simply follow the recommended route. We have essentially done just that, but with one major exception – we have not used heat pumps.
Our main family car is now an EV; we have double glazed the house; we have installed 8.5kW of solar PV; we have turned off the gas. We are now well on the way to becoming a fossil fuel free family. I have documented our energy transition process and produced a book called Our Household Energy Transition: Becoming a Fossil Fuel Free Family. Heat pumps just did not add up for my family.
Heat pumps are favoured by the pundits because of their remarkable energy efficiency. However, when researching the options for replacing our gas-fired space heating and hot water I became concerned that many of our energy experts appear to be almost mesmerised by heat pumps and show no inclination to consider alternatives. In my view, if there is going to be a widespread community movement away from the use of gas in the home we should be looking to expand, not close down, the number of sustainable options for space heating and generating hot water.
Tackling space heating first. The main reason we did not replace our flued gas central heating system with heat pumps was primarily because we already have a heat pump in one of our rooms at home and my wife i
I eventually came across far infrared (FIR) heating panels. I was not aware of these when I set out on my search but have found them to be quite remarkable (they should not be confused with conventional (convection) panel heaters). Initially I was very sceptical of the claims made about FIR panels, but was intrigued enough to buy a low powered (600W) panel as a trial. On the basis of this trial we have now installed four larger (1,200W) panels on the ceilings in our two main open space living areas. They look very much like whiteboards (other options are available) and do not change colour when they are turned on (see picture). They deliver a lovely pleasant low intensity radiant heat and generate a feeling akin to sitting in weak sunshine on a winter’s day. They are both very efficient and very effective.
Moving on to hot water. In this area the pundits seem to be less dogmatic; heat pumps seem to be the preferred option but solar collector systems are acceptable. I began my research by getting a quote for a heat pump hot water system and would almost certainly have gone down that route except that I would have had to locate the unit very close to my neighbours’ house and I became concerned about potential noise problems. I spent more than 30 years as an environmental bureaucrat and was associated with environmental noise control all that time – I was acutely aware of the nasty circumstances that can arise when noise from fan/compressor units disturbs neighbours.
I thought about installing a solar collector system but since we were already exporting a great deal of electricity that could be used to heat water it made no sense to install a separate solar hot water system. In the end, we simply installed a standard resistive element/storage tank system and fed it with our solar PV electricity. In order to ensure our solar PV was diverted to our hot water system effectively, I installed an energy diversion device (an Immersun unit) – this combination means that we are now getting at least 95 per cent of our hot water from our own solar PV electricity.
In summary, we have not used heat pumps for either space heating or hot water in our energy transition but have been able to achieve excellent energy/carbon outcomes. We h
In heating, we have attained a thermal comfort which is far superior to that provided by heat pumps. With hot water, we have avoided the potential for noise disputes with our neighbours. I provide the detail behind these claims in my book which I mentioned earlier.
The bottom line is simply that just because heat pumps offer the most efficient solution, it is not necessarily the best solution. We need to consider both efficiency and effectiveness. Let’s keep our options open and provide a suite of low carbon measures for households to choose from when they head out on the road to fossil fuel freedom.
This post was published on February 16, 2016 11:37 am
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HI Dave, was wondering if your immersun is setup to dump loads into the panel heaters as well as the HWS?
Hi juxx0r. I could set the Immersun up to divert my solar PV electricity into the FIR panels but have not done this because I don't believe the heat put into the rooms during the day (absorbed by furniture etc) would be retained long enough to help with heating in the evening. Even in winter here my water is usually hot by noon so any heat would need to be retained for up to six hours. If you look at my book which I refer to in the article you can see that last winter I diverted electricity into a storage heater once the water was hot. If I need heat during the day I just turn on the FIR panels and on most days, since they draw little power, they will be fed by my solar PV.
Thanks Dave.
I live in a circa 1930's house of infinite draughts. Even with the lack of airtightedness, i still get about two days of thermal storage in the brickwork. I can tell this because i dont run aircon or heating and it takes two days for changes in weather to accumulate so you should get a win if you're only looking to store heat for 6 hours.
Interesting point. It sounds like you have a solid brick house with plenty of thermal mass (similar to Europe where FIR heating is much more common). My house is just a wooden framed house with plasterboard - very little thermal mass. Based on my experience so far with the FIR panels I guess that on a cold winter's day in Canberra if I heat up a room to say 20 degrees C with the FIR panels and then turn them off the room will return to its original temp in about 2 hours. If I did the same with a fan heater it might take 30 mins to get back to its original temp. I plan on running some tests when winter comes to try and get a better handle on heat retention times.
Oh. that sucks. Another good reason to go with the FIR.
HI folks: If you want to debate / investigate heat pumps vs other things on Facebook, this Discussion Group could be for you.
https://www.facebook.com/groups/996387660405677/
I am certainly interested i what Dave is writing above.
I think using PV to directly drive hot water has promise, and using radiant panels is also interesting and valuable. However the article conveys some misunderstandings about heat pumps. It says "we should be looking to expand, not close down, the number of sustainable options for space heating and generating hot water". Using heat pumps is entirely consistent with this goal because heat pumps harvest renewable ambient heat.
I agree we should be mindful of potential noise issues, however many heat pumps operate with very low noise levels. It's problematic to suggest that heat pumps generally represent a noise problem. One good heat pump unit I've dealt with, the Sanden hot water system, is so quiet it's almost uncanny.
The other point here is the suggestion that heat pumps can't contribute radiant heat. Sure most don't directly, but some do. See the Daikin Nexura for example.
I think we're in violent agreement. I'm not opposed to the use of heat pumps - they are indeed a wonderful sustainable option. I'm keen to find additional low carbon ways of space and water heating - I just believe we should not be focusing on heat pumps at the exclusion of other viable options .
If you don't already have a H/P for heating water I wouldn't waste PV output on a resistive water heater. The most efficient way of heating water year round over any H/P is an Evacuated Tube Solar collector. Even though the Sanden units are cheaper to run than a resistive storage unit they will still suck down on average 3kwh/day and more in winter.
My Edson ET only required boosting 10 days in 2015, using no more than 60kwh v's H/P 1,100kwh p.a. And average ET collectors only uses 4.2sqm of roof space. Saving room for more PV which can power the A/C on those nasty hot days.
As for space heating H/P is the only way to go but, get a Dakin if you can afford it, if not, Fujitsu have models with a COP of 4.9. What ever you do don't get a ducted A/C, get splits. far less losses.
Hi Solarguy. Can you tell our listeners in what region of Australia you live? Thanks!
Hunter Valley NSW.
Thanks Solarguy.
Yes, rooftop-solar-thermal-hot water will require more winter boosting in climates that, compared with your location in the Hunter Valley NSW, are colder and/or receive less winter sun.
Thus hot water heat pumps (just another form of mostly-to-100% solar energy really) tend to be favoured in climates such Melbourne.
And hot water heat pumps are a good fit with solar PV as described here: http://reneweconomy.com.au/2015/get-more-out-of-your-solar-power-system-by-using-water-as-a-battery-26228
Tim, Let's compare apples with apples here, a general reference to SHW could infer any SHW system, but I'm not talking about any other type, only Evacuated Tube Solar. Not flat plate collectors, the difference is chalk and cheese between the two, with ET collectors being vastly superior in performance, particularly in winter when you need it to work.
As ET collectors aren't effected by ambient temperature like flat plates or even HP'S are, ET'S will boil water in Antarctica as long as they receive enough solar radiation and will even produce usable heat on light overcast days.
As I understand it SANDEN HP will cut out at 60 degrees, where even on some partly sunny days ET's can achieve 80. If HP's were set to cut out at 80 they would require more coal fired electricity.
Correctly sized for it's winter load, ET systems perform very well in Melbourne. That's why they love them in England and the Continent. Even if you had 40 useless solar days in a year ET's would still out perform H/P's. Far and away better.
Tim, no where near nearly to 100%. If you have to use that much energy to utilize a diffuse resourse.
Tim, don't you mean readers.
I have a Sanden hot water heat pump and it is eerily quiet. Many visitors are astounded at how quiet it is. I'm planning to install a Daikin US7 heater air conditioner, as I have several friends who have them and recommend them. I plan to operate it during the day to pre-heat and pre-cool the house using excess solar PV. With properly insulated walls and double-glazed low-e windows, the internal surfaces of the living room (being built now) should be in similar enough to the air temperature so that the room doesn't feel cool. These highly efficient appliances are valuable as I expect that they will allow me to run my house entirely on solar (with a small battery) even in winter, when solar yield is low. I can only fit 5 kW solar on my roof, unlike Dave's 8.5 kW. If I used an Immersion or FIR panels, I'd have to import power from the grid during winter.
Even so, I use a small 600 W radiative heater in the bathroom, as it works even when the exhaust fan is sucking out all the hot air. The heater runs on a 30 minute timer, so it won't use too much energy. To work effectively a radiant heater needs a high surface temperature, e.g. > 200 deg C. The more efficient radiative heater panels have a black highly emissive surface. Such devices can be seen above cafe outdoor tables. The white surface in Dave's model suggests that the surface temperature is low, < 60 deg C, so I expect it's not as efficient as it could be.
Dave - have you tested or inspected the Sanden hot water heat pump or the Daikin US7? Can you measure the surface temperature of your FIR heater?
Very interesting. The idea of pre-heating and pre-cooling rooms with solar PV is fascinating! I'd be very interested to know how you go doing this with a heat pump. As I said in my comments to juxx0r, my place has such a low thermal mass, and is very leaky, that I suspect any heat I input during the day will dissipate quite rapidly. The heat injected by a heat pump, which essentially just heats air (which then gets transferred to objects), would, at least at my place, rapidly disappear through the walls, windows and ceiling. The FIR panels which are directly heating objects, not air, would seem to have a much better chance of being able to be used for pre-heating. I probably would do some pre-heating if I was getting nothing for my exported solar PV but by pre-heating I am foregoing an income of 7.5c/kWh. Anyway I will trial this some more during our coming Canberra winter.
I think its important not to confuse visible radiant heaters (I have these in our bathrooms; they abound in Canberra restaurants) with FIR panels which are radiating in the non visible part of the spectrum. The surface temperature of the FIR panels is about 100 degrees C. I find the FIR panels amazing. Not only are they wonderful as personal heaters they are also brilliant as room heaters (this really surprised given the low power ratings involved). The heating effect is in no way comparable between the two types of radiant heater.
I am aware of the Sanden hot water heat pump - I had a quote for one of these when I was going through our energy transition. Incredibly impressive specs. After having spent decades working in environmental noise my only comment is that very nasty noise disputes can, and do, arise over the operation of equipment that is barely audible. Hence my concerns about installing one of these.
I'm not familiar with the Daikin USS7.
Here is our Daikin Ururu Sarara (US7) story.
http://renew.org.au/sustainable-houses/comfortably-ahead-a-tale-of-two-heaters/
Hi Dave: I just scanned your book. Thanks for the contribution!
1 question: Looks like you are getting by without any space cooling in your light-frame house, is that right? How do you manage that? How warm does your house get say after some consecutive hot days in the ACT? I am Melbourne based so may not fully understand the ACT summer climate.
During a hot spell most rooms in the house get to around 28 degrees C. Maybe we're mad but we quite enjoy having these short hot periods - makes up for the low temperatures for the rest of the year! We do use low power (40W) fans in some rooms on some nights. I put the main reason why our house is relatively cool is the orientation and the window arrangement: nearly all the main windows face east. We have very few windows facing west and south and only one decent sized window facing north. Not good orientation for the heating season but I find it great for summer - it's nice to wake up to the sun; the nights are generally reasonably cool in Canberra; our patio area is to the east of the house and this is generally in the shade by around 11am on hot days.
Thanks for that. I shall study you book in more detail!
Here is a recent article discussing heat pump heating:
https://stepoffthegrid.wpengine.com/hot-summers-nights-cold-winter-evenings-how-to-stay-comfortable-and-save-all-year/
And one discussing heat pump and solar PV water heating: http://reneweconomy.com.au/2015/get-more-out-of-your-solar-power-system-by-using-water-as-a-battery-26228
Dave, I recommend that you do a Blower Door pressure test to find air leaks in the house. The comfort gain from that measure is tremendous and translates into big energy savings. It's a cheap and easy task.
About the economics of weatherizing read more on
http://www.iwilltry.org/b/projects/weatherproof-your-home