Winter in an all electric home
An account of our experience through winter in an all electric house in Kyneton. I hope to give you a view into some of the ways in which I'm trying to reduce my energy usage through automation and self-solar use, while staying warm and healthy in the relatively cold climate of the Macedon Ranges in Australia.
In this post:
About our setup
Kyneton, in Central Victoria, Australia, is cold over winter. Temperatures regularly drop below zero in the morning, and most days during winter and much of autumn and spring, our temperatures are around 10C less than they would be on the other side of the Great Dividing Range - a mountain range that separates a more coastal, temperate climate, from our more inland cool climate.
This means that homes in the Macedon Ranges require more energy to heat and cool than those closer to the coast, which means higher energy costs whether that's through fossil gas or electricity.
About 2 years ago, we electrified our house and removed our dependency on gas. Our family of 4 now relies on:
- 1 x ducted 12.5kW Mitsubishi electric reverse cycle air conditioner (PEAM125HAA) for the new part of our house, which uses insulated ducts and is zoned. Wifi connected.
- 4 x smaller 2kW Daikin (1)and 3kW Mitsubishi Electric (3) reverse cycle units - one for each bedroom and one for a small study. All controlled by Sensiblo wifi controllers.
- A dehumidifier for the laundry. On a KASA wifi plug
- Heat pump dryer
- Top loading washing machine
- A dishwasher.
- Underfloor heating in two tiled bathrooms (resistive, not hydronic) + heated towel rails.
- 2 x 750w/1500w resistive Vornado blow heaters. On KASA wifi plugs
- A Reclaim CO2 heat pump and 315L stainless steel Earthworker tank.
- Induction cooking and electric ovens.
- A fridge and a deep freezer.
- Networking equipment and some wireless access points.
- A few LED garden lights. KASA plugs
- Electric blankets
In order from to bottom, these items make up the vast majority of our energy use over winter.
Contributing to our energy we also have 13kW of solar panels coupled with a 10kW inverter (with energy monitoring) and three phase power. We built our roof so that the majority of these panels would face north, but we also have a smaller number facing East and West. This extends our generation bell-curve and delivers a more usable amount of power earlier in the morning and later into the evening.
Our house has a footprint of about 100m2, but has a door to seperate the new living spaces from the old bedrooms. This can be shut to conserve heat on weekdays. This is likely to be hotly contested but we chose a black roof to contribute to warming our house in winter, as opposed to a light roof to aid cooling in summer. We also didn't want have the funds to replace the old roof (which was green), so painted this instead of reroofing. Ultimately I think this makes sense, because, as you'll see, we use way more power in winter than summer. Optimising to reduce winter usage makes sense – if we can soak up a few degrees of free heat during the long winter, this reduces the amount we need to buy from a largely dirty grid.
Alongside the changes we've been able to make to our house itself, I've also been exploring ways to reduce energy use while maintaining comfort using Home Assistant. Home assistant is a raspberry pi based home automation platform that allows you to stitch together of disparate devices and systems into a single system you can use to control them. More on what I've tried using home-assistant here. Thanks to the energy metering on our inverter and Home Assistants' energy monitoring features, I'm starting to get a pretty good handle on when we use power and how much we're using. Here you can see almost a full years' worth of usage.
We use a lot more power over winter (June-August in the Southern Hemisphere) than summer (December-February). In summer we export at least as much as we import, whereas in winter, we're purchasing the vast majority from the grid.
On average this June we used 61kWh per day. Only 24% of this was provided by solar, so all up we purchased 1,399kWh from the grid and exported only 163kWh. Compare that to January in summer, when we used an average of 36.5kWh per day, of which 69% was provided by solar. In January we only purchased 347.5kWh from the grid and exported a whopping 1,463 kWh.
A week in winter
A week in summer
My summary of our energy use would be that we're actually not doing badly at using our own power over summer – we just make too much of it and it's far less energy intensive to cool than to heat, so we export a lot. In the future we plan to soak much of this up into a battery or electric car. In winter though, we've got a bit of a battle on our hands. Most of our power use happen either early in the morning as our heating turns on, or early evening after the sun has set (and during peak power pricing). Solar largely takes care of the middle of the day, but also, this is when there's usually only one person at home.
How much does power cost anyway?
At current rates, during winter we spend approximately $200-300 per month on power. However, from August 1 2023, Momentum (and many other Victorian retailers), will be dramatically increasing the cost of power. This makes finding ways to use less enery even more important.
- Supply charge (daily): $1.2452 → $1.287 (10.3% increase)
- Peak 3pm - 9pm usage ($/kWh): $0.2651 → $0.4048 (52.7% increase)
- Off-peak 9pm - 3pm usage ($/kWh): $0.1507 → $0.2629 (74.4% increase)
What is a peak/off-peak tariff?
We swapped to a peak/off-peak tarrif model recently as Momentum suggested that we'd save some money doing this. My understanding is that the government mandates that retailers tell you if you can get a better deal with them, so login to your account every now and again to see if there's a message. We now pay a higher rate from 3pm in the afternoon until 9pm (6 hours), and a lower rate for the rest of the day (18 hours). Up until recently this meant that that early morning heating was a lot cheaper than it will be after August.
But what about gas?
We precariously don't currently pay a gas bill after having been advised by Momentum that if we closed the tap on our meter and cancelled our account, we wouldn't be slugged with a daily supply charge. Time will tell if that was good advice or not. The recent news about capping the cost of meter removal is a welcome clarification to the shit-show that existed before, although it still doesn't feel like that's been fully resolved for consumers.
Maybe gas companies felt until recently they'd be able to make a come-back one day (with hydrogen?), but I see that as pretty unlikely. I'm considering finding a way to get a gas company to remove the meter and cap the gas pipe, but I'm definitely not keen on digging up the entire garden to remove a pipe that does nothing so for now, it's easier just to leave it where it is.
Maximising solar and off-peak power
They say that the cheapest energy is the energy you don't have to use, so with that in mind, now that we've electrified, double glazed and insulated as much as we can, my efforts have turned to both reducing overall usage, but also to maximising solar use. Given the value of it is so low, I almost entirely discount solar export as providing any meaningful reduction to our powerbill given we are paid 5.3c/kWh (an 8:1 ratio with peak power or a 5:1 ratio with off-peak power, which is frankly outrageous), so self-consumption is the name of the game.
Below is a list of the things I've experimented with so far, and how those experiments have fared.
Heating our house during winter is, by far, our biggest user of power. Our house has two zones - a daytime living zone heated by a larger 12.5kW zoned ducted system and an almost equally sized bedroom area. Each bedroom has its own 2 or 3kW split system. A seperate study has a 3kW split system.
On weekdays, I can close the central door dividing the bedrooms from the rest of the house. This has the added benefit of making it possible to watching loud movies at night.
To double down on only heating the areas we're in, if it's just me at home I can turn off all the heating except for the study (with it's single split system). This frees up solar power to divert towards the laundry, dishwashing and water heating. Most winter days, we make enough during the day to power the study without consuming much from the grid.
Individualised bedroom temperatures
Use the individual split systems in the bedrooms lets each occupant sleep at a different temperature (within reason). Most of the time, we prefer to sleep quite cold and our rooms sit between 13-15C overnight. When someone is sick though, being able to heat a room up a fair bit higher is really invaluable to helping that person get better, faster. If we had to do this for the whole house, some people would be too hot and we'd use a boatload more power. Sometimes you also just get sick of being cold and need to warm yourself up for a bit.
Less expensive replacement cost and redundancy
Things innevitably break and need to be replaced and split systems are no exception as we found during our renovation. By having our heating spread across multiple units, we don't need any particular piece to work as hard and as frequently. Hopefully this means the HVAC units will last longer. When one unit dies, we can simply replace that single inexpensive unit versus having to buy a new mega unit. While expensive, the individual HVAC units for our smaller rooms are way less expensive than having to replace the ducted unit should they die.
Obviously, smaller units are also much cheaper to run if you're using them to heat an appropriately sized space. Importantly, HVAC systems have a minimum operating range - which I think means that if you have a 3kW Split system, and it's minimum operating threshold is 10%, you'll use 300W no matter what if it's running. This is why having smaller units is so beneficial – 10% of the 12.5kW ducted unit is 1.25kW, so costs about 50c per hour to run at a minimum. Coupled with the fact that it never actually runs at 10%, heating becomes quite an outlay. That said, our ducted system keeps us warm in winter and cool in summer, and is still cheaper than gas, so I love it.
When you get your kit off to hop in the shower, things get pretty chilly. Having underfloor heating warming up the tiled floor in the morning is a lovely (total) luxury, but it's way too expensive to keep running all the time. It does also have the advantage of drying off the bathrooms after they've been used, which is important.
Given we all have showers at different times of the day, we have some small resistive blow heaters (Vornado) connected to Kasa switches. This way when someone wants to have a shower, they can ask Google to "turn on the bathroom heater". This way we're only warming up the room when it's actively being used.
For the rooms that don't have split systems, I've found that if it's just me watching TV in the evening, it's more efficient to use a smaller blow heater to warm up the single room I'm in than to use the ducted system (around 750W versus 3000 - 7000W depending on the outside temperature).
I did consider buying an electric throw rug to put over my legs at night and in the study during the day, but worked out that I'd need to use it for several hundred hours before it would pay for itself in saved electricity. I doubt that they'd last that long, but that equation likely changes with the recent price hikes, so it's something I'll look into. Personal space heaters are obviously far more efficient than heating a large volume of air, however, there is also a quality of life trade-off to be made. My wife is a dog trainer who spends a lot of time outdoors, and she swears by her heated jacket.
Mould and mildew
While you could argue that doing anything other than using personal space heaters like throw rugs or heated jackets is excessive — just put on another jumper — the other really important consideration when living in a cold climate is reducing moisture in the air and preventing mould. Just by existing in a house you're adding moisture into the air both from breathing but also from cooking, laundry, boiling water. If your house is cold and damp, it's only a matter of time before mould starts to grow. Keeping the materials and furnishings dry is essential.
There's a direct relationship between the temperature of the air and the amount of moisture it can hold – this is why global warming causes more savage rain – hotter air can hold more moisture so you experience less "damp" whereas colder air deposits moisture onto surfaces more easily. Drying clothes indoors and wet bathrooms aren't great for this.
There's also the need to balancing quality of life with cost and environmental considerations. Who doesn't want to live in a healthy, warm environment? The WHO recommends that the inside of houses should be above 18C for health and hygiene. We would get to that temperature most of the time during the day thanks to sunlight, but overnight, keeping our bedrooms at that sort of temperature requires a lot of energy. In the chart above, you can see energy use slowly creeping up towards dawn when temperatures get coldest.
We don't personally find it comfortable to sleep at 18C, but I'm still very keen to make it so that our house doesn't stay cold all the time to keep mould and other health issues at bay. It undoubtedly also helps with mental health to not be constantly freezing. If it's a sunny winters day, I'll crank all the heaters to soak up solar and dry everything out for a few hours. Home assistant makes this super easy and sends me alerts if we're exporting enough to do this.
Our hot water system is a Reclaim Heat Pump with a 315L tank). It has 5 or 6 different settings that allow for the heat pump to activate at different times of day depending on your preference. Their new models have wifi control, which is awesome, but unfortunately you can't just buy the controller without also upgrading the heatpump unit (I asked 😭).
Option 4 is designed to maximise solar PV self-usage. It tells the heat pump to turn on at 10am and run for 6 hours or until 57C is reached. 57C is the magic number needed kill legionnaires bacteria. Swapping to this mode from Option 1 (which runs as needed 24/7), has been a good move for us 95% of the time. Combined with the insulated 315L tank, we very rarely run out of hot water.
To avoid family turmoil (and needing to go back to option 1), I've tried to minimise the chance than anyone in the family has a cold shower other than me. It takes a remarkably long time to use all 315L of hot water (remember it's mixed with cold), but with two younger kids sometimes a lengthy shower session means the next person gets an unpleasant lukewarm surprise. Fortunately, it tends to be me having a shower in the morning. I'm in awe of the insualtion on the Earthworker tank - it's amazing that it stores all that water at a really hot temperature until the next day. I've never had better showers.
A few months ago I experimented with changing from option 1 to option 5 as option 5 allows me to set two "on" periods instead of one. I set it to:
- Do the same as option 1, but from 9am for 6 hours instead of 10am (finishing at 3pm before peak tariff)
- Fire up again at 9pm for 1 hour (to use off-peak power to ensure there is always just enough hot water in the morning)
Because heat pumps harvest heat from the air instead of heating using an element, the colder the air is outside, the harder and longer they have to work to provide the same amount of hot water. I suspect that on cold days, our hot water heat pump works pretty hard, but so far it's not failed us – the water coming out of it is easily hotter than our old instant gas service.
I also think I was asking a lot of it by asking it to heat at 9pm when the ambient temperature in Kyneton is already cold and frosty. Recently I noticed that the fins on our unit have started developing a little algae type growth on one side. Reclaim's support was really responsive and not worried, but the options they suggested to try and fix it weren't really that feasible. I can't move the unit further away from the wall without a plumber and don't really want to spend money on professional cleaning. I suspect this algaue growth has happened because of the 9pm use. Turning on the unit early evening potentially sucks in more dew than it would if used during the day.
To avoid any more growth I've recently swapped back to Option 4 (but I haven't told anyone 🤫 in the family). I'm hoping that along with some chats to the kids about not having showers that are tooooo long (I'm pretty sure the water restrictions will come soon enough so I don't want to do this until we have to and while dams are full), our hot water should be predominantly solar / off-peak powered.
Pro-tips for Reclaim units:
- If you find your HWHP is running all day, check the thermometer probe. Initially ours was not seated deep enough into the tank, which meant the control unit thought the water was cooler than it actually was. This meant it kept gunning the heat all day, using a lot mower power, but also making the water dangerously hot. It was an easy fix to push it more deeply into the tank.
- Reclaim units have a boost button (great for heavy use for a short period) and, I believe, also a 12V trigger that can be used to start the unit when enough solar is being generated. Making use of this requires that you have a wired connection from an appropriate inverter to your hot water controller. In my case, the juice wasn't worth the squeeze here given I could use Option 4 and get most of the benefit. The extra cabling and electrical cost wasn't worth the savings. I had wondered, however, whether it would be possible to retrofit the 12V trigger in conjunction with a Wifi connected device like an ESP32, to trigger boost mode during solar production or hot water generation when a particular minimum temp is reached. Fortunately, the new Reclaim controllers look like they actually have all of this built-in.
- I think installing heat pump hot water is a relatively new thing for most plumbers, builders and electricians…and you need all three of them to be working together to do it well. If you're getting one installed, you'll need to have both an electrical line for the heat pump, but also a standard outlet for the controller. We got lucky in that we had one left over from our retired instant gas hot water. If I had more time during our planning here, I'd have moved the controller unit into the laundry or bathroom instead of being outside exposed to sun. That would make using the boost mode easier and increase the working life of the control unit, which feels like the weakest link. Microelectronics, even in a IP67 container, probably won't last as long as a tank or heat pump in the hot summer sun and cold winter rain. Time will tell.
- Allow as much clearance around the heat pump unit as you can to give it room to breathe. Heat pumps need to suck in, and blow out a lot of air. In summer, I wonder if there's a way to ….reclaim… some for the cool air output by the hot water heat pump and harvest that straight into the air conditioner heat pumps (working in the opposite way). The same in reverse with air conditioners blowing out warmer air that could be harvested by the hot water heat pump. It feels like, with the ability to do some seasonal diversion, there'd be a way to make it so that these units could work in more efficient tandem with each other as they have opposite input requirements. Maybe some removable ducting could help? Has anyone tried this? I see a series of tubes in my future.
We do a lot of laundry.
I don't have the data to back this up, but we must use easily as much water doing laundry as we do for showers. With four people going through at least one change of clothes a day (my wife gets muddy-pawed by dogs frequently), on average, I'd estimate we we generate a large load of washing a day.
Our relatively old Westinghouse top-loader washing machine is pretty water and energy inefficient, but it is an absolute workhouse. We've had it serviced a few times and different repair technicians have independently told us that they don't make washing machines as durable as ours anymore and that we should keep it going as long as we can. I'm not sure if this is a fallacy or not, but for now, that's what we have. My next challenge will be reducing our water usage, so we might end up with something more efficient at that point. For now though, we're being stretched in too many other directions, so the old washing machine stays.
Drying washing indoors over winter…without growing mould.
For the most part, hanging washing outside in Kyneton over winter, with very few sunny-day exceptions, is an exercise in futility. Once we've done the washing, which I tend to do on sunny days earlier in the morning so that I use the hot water stored, hottest loads first, followed by cooler loads, we now have two drying options in winter.
Wwe installed a outdoor clothesline in our relatively small laundry The laundry also has an exhaust fan, which I think is relatively essential, as it can be used as a low cost way of sucking warmer/dryer air from the rest of the house past the washing hanging on the line and pushing that moist air out of the house. On warmer days when there is sun streaming into the house, this is a pretty effective way of getting things dry.
For the cloudy cold days the laundry has a ducting zone that can be turned on and off. We don't turn the ducting on just for the laundry as it's too energy intensive, but if it's already on for the other zones, then the HVAC provides the most efficient heat source because of it's COP.
The majority of our drying power comes in the form of a dehumidifier. We run this under the clothesline and it's great for more delicate and elastic items (like socks, undies, bras etc). We recently also got a heat pump dryer which is good for things like shirts and towels. It takes a few hours, butbecause it only uses 600W, this is actually a feature, not a bug, because it means it can work off solar even on cloudy days. It's not great for sheets though (they bundle up on themselves), so they go on the clothes line. Running the dehumidifier and dryer during the day when it's sunny means we get a lot of this drying for free even though our power use is high. We also occasionally take the dehumidifer into our bathrooms to dry them out on sunny days. It's amazing how much moisture can still come out of the air.
The dehumidifier is powered by a Kasa plug, which turns it on and off depending on whether there's wet washing hanging out. The Sensibo units I've got for the bedrooms came with a secondary motion/temp/humidity sensor, so I can use this sensor in conjunction with a Home assistant "Wet Washing Hanging out" button to only turn the dehumidifier on when we've got washing to dry.
To speed up the drying process for the clothes line, in conjunction with the dehumidifier, I've set up a small 750/1500W blow heater that automatically turns on in the event that it's particularly sunny and we're exporting more than 750W of power (only if I'm at home).
All up this seems to be a pretty effective way of drying a large amount of washing in a short amount of time. Yesterday, for example, I did five loads and it was all mostly dry by the end of the day and we don't have any mould or humidity problems in the laundry, which is great. We also don't have washing strewn throughout the house most of the time, moistening the air.
I hate washing dishes but love cooking so we're pretty dependent on our dishwasher. We try and do a load in the middle of the day if the dishwasher is full to soak up solar. If we need to run a load in the evening we use the little Hour + button to set the dishwasher to come on after 9 when the off-peak tariff starts.
Getting off gas meant swapping from a fossil gas cooktop to induction. For the most part, it's been a great move.
We'd decided to make the move before the news about the adverse health effects of having a gas stovetop – indeed, at some points early days in our leaky weatherboard cottage, we used the burners as our primary heater. I hate to think what damage that potentially did to my family and wouldn't go back to having gas indoors again.
An induction electric cooktop was one of the more expensive pieces of our electrification journey, both because the stovetop was expensive but also because to support it's peak 11kW draw (along with everything else), we needed to upgrade our power supply to three phase.
All said and done, induction has been mostly great. We're able to cook just as, if not better, than before and don't miss gas at all. I've broken down some of the pros and cons.
The pros of induction cooking
- Great temperature control - our model has 13 levels of heat and really precise temperature control. This fidelity means you can melt chocolate directly in a pan or sear a steak. It also means that with a bit of pre-heating and a flat bottomed wok, stir-fry is also possible. I've even used induction to season a wok.
- Induction gets the base of pans really hot, really quickly. You can re-use your existing pans if they are ferrous (and a fridge magnet sticks to them). Cooking with thicker cast iron, for example, means you can get a really hot surface and keep it hot for longer. I've seared a steak better than when using induction.
- The cooktop itself is really easy to clean as they're basically a flat glass surface. Cleaning is just a matter of spray wipe – a stark contrast to the mangled mess that would accumulate around our gas burners.
The cons of induction cooking
- It could be unfounded, but I don't feel like our Asko induction cooktop will last super long, despite being almost $6k full-price (we got ours at half that cost through the Asko Deals shop, which sells ex-demo units). We've noticed a tiny chip in the surface itself and Asko's customer service is pretty woeful. We've since bought a protective fibreglass matt to sit over the chip, but it'd only take one slip of an oily bottle or an exhaust grill to smash the glass. I wonder if glass cover as part of home insurance would cover the cooktop being smashed?
- The capacitative touch buttons used to control the cooktop are very sensitive to being wet or oily. This is problematic if you're boiling water and it bubbles over beacuse the hobs are so powerful. If drops overflow and hit the buttons, you need to dry it off and reset everything, including timers. This is obviously a safety feature, and I haven't seen many induction cooktops with physical buttons. When I get the next cooktop, I reckon I'd do my hardest to either get a separate control unit that is physically distanced a bit from the cooktop, or one with more tactile buttons.
- Induction doesn't make the air around your pots hot because it's efficiently heating the base of the pan itself…not the air, then the pan as gas does. This has the odd implication that the exhaust fans and exhaust grills don't get warm. The problem with this is that condensation forms when hot steam hits cold metal. Despite having a really good Schweigen exhaust system, we often get drops of water combined with oil dripping back off the grill and onto the cooktop (sometimes into the dish wer'e cooking, which is gross). Combined with the sensitive capacitative controls being set off by drops of water, this is particularly annoying, but fixing it is difficult. Perhaps models that suck exhaust downwards are the way to go, but I'm sure they have their own downsides.
- The only thing we can't cook on induction is rice. I think this is to do with the starch in rice bonding to the hot metal in the pot more directly and quickly that it would when using gas. Fixing this was easy though, we bought a rice cooker, which is great.
- Almost all the images you see of induction cooktop installs omit a very important detail in their pursuit of presenting a minimalist aesthetic. This detail is ventilation. Induction cooktops consume a lot of electricity, and use magnets to heat up the pans' metallic surface, but they also need to dissipate a lot of heat to keep their electronic components cool. Reading the MEEH after our install, I noticed a few people complaining that their induction hobs had died prematurely, but that their warranties were voided because they'd been installed with insufficient ventilation. I checked the installation manual for our specific model and found that it also contained some pretty cryptic instructions specifying the ventilation requirements. Obviously this had been overlooked by our builder, electrician and cabinet maker, so ventilation requirements aren't widely appreciated, but seem to be important. We haven't done anything about this yet and are hoping that small gaps around the ovens immediately below our cooktop provide enough airflow to get enough air in and out. Time will tell.
Reading this back to myself it sounds like I'm anti-induction cooktops, but really I'm not. They're great, better for cooking than gas and easier to clean.
Some pro-tips for anyone getting one for the first time:
- If you can, get it recessed into the bench itself so the sides are protected from hits on the edges. From what I've seen most induction cooktops get broken when hit on the side of the tempered glass because that's their weak point. Consider also getting a commonly sized induction unit so that it can be replaced with an alternative if it breaks in the future. This might actually be an argument against recessing it as well. We didn't get ours recessed.
- Do some research into downwards ventilation systems versus ones that draw air upwards. I didn't realise this issue existed and how annoying the drips would be.
- We actually use the 6 zones on our cooktop at the same time quite often as we like to cook, but it's significantly cheaper (including reducing the maximum amount of electricity you need) to get a four or two burner unit.
- We found that the Bunnings $69 induction units are not a good representation of what it's like to have a good quality installed unit. We had one of these for use while we did a renovation and it had none of the temperature control finesse and was noisy. Still better than a gas stove though.
- Consider having a backup source of hot water and ability in the event of a power failure in the event that tea or coffee is more important to you than life itself. We've got a kettle but also a fire pit and BBQ in the event that a power outage knocks out our grid. This has happened a few times now and I can't imagine it won't happen again. You're unlikely to be able to power an induction stovetop with a generator unless it's massive (and probably therefore expensive).
Using automation to maximise self-consumption
Now that we're fully electric, alongside changing our habits, there's lots of automation we can do to maximise solar and minimise grid use.
Not all things are equal when it comes to automation - tapping away to manually set up a schedule on a wall unit is a PITA and therefore less likely to be changed regularly than a service you can adjust using a tool like Home Assistant or an app. Similarly, within the options we have for heating, some are far more instantaneous than others. Yes, HVAC systems use less power to generate the amount of energy, but they need a bit of time to start up and, I've read, don't appreciate being used for 5-10 minutes at a time. A resistive blow heater doesn't really care and is also much cheaper to replace should it die from more frequent stop/start usage.
All this combined means I've used Home Assistant pretty extensively to manage, and ultimately reduce the loads I can.
Bathroom and towel drying
The controllers for our bathroom floor heating, and towel rails are wall units that can be programmed by tapping away at them. It makes sense that these are set and forget sort of operations based around our families habits. At the moment our underfloor heating is set to come on at about 5 am and pre-warm for the morning school run chaos. This is the only predictable time during the day that the family uses the bathroom, so it's the only time that it turns on.
Assuming that people hang their towels on the towel rails in the bathroom they are heated to dry them during the middle of the day using solar. On days when it's cloudy it’s still important to dry the bathroom out, so these turn on regardless. They’re also too difficult to change based on weather conditions in solar generation. If I could get a wifi controlled version I probably would, however I couldn't find one at the time.
Giving our ducted system a brain
Our ducted system is a Mitsubishi electric reverse cycle unit with insulated ducts and three different zones. One for the laundry, one for the living room and one for our rumpus room. While it does have a temperature sensor for the living room, it was too expensive to install temperature sensors in the other zones.
A gotcha with ducted heating is that you need to have the primary zone with the return air vent turned on at all times so that the air can be recirculated. In our setup, while individual zones can be turned off or have their vents partially closed, I’ve found this is not something that happens automatically as a result of attaining the right temperature. I’ve also found that even the Living Room, which has a temperature sensor, doesn’t cause the unit to turn off or throttle down significantly even when the target temperature is reached.
Fortunately, the system is driven by a tablet running MyAir, which is a proprietary home automation system that happens to have an open API. Some lovely person has created an integration for this system into Home Assistant, which means I’m able to turn it on and off using a Sensibo temperature sensor.
At the moment, this set up means that overnight, the ducting is turned off but it's turned on again in the morning so the house is not cold when we wake up. Fortunately this part of the house is relatively well insulated and doesn’t cool down as much as the old weatherboard section overnight.
During the day the temperature sensor turns the unit back on again when the temperature drops below 18° and then off again when it gets above 20°. As reverse cycle systems don’t like to be turned on and off super frequently, there is a duration timer that only turns the ducting off after the temperature has been reached for 10 minutes or so. In reality, this means it’s turned on for 30 minutes to an hour at a time.
While all this sounds efficient, the morning heat up cycle is by far our single biggest use of power on every given day. You can see it in this in the average daily energy use chart above. That spike…that's ducted heating.
Nb: It’s worth noting that I have also experimented with simply leaving the unit on at a lower set-point – say 17°C – but I found that this used more energy overall. It may be that are unit is not properly configured to turn itself off when the temperature desired is reached, so I’ll chase up with our installers. It may also be that I need to leave the unit on for several days to let the surfaces themselves heat up to the point the retain more heat. It feels counter-intuitive, but there might be something in it.
Using Sensibo climate react to reduce usage overnight.
Each bedroom has a split system. One of the most useful ways to curb energy use here has been to use the relatively inexpensive Sensibo controllers to control the HVAC units, and to automate setting comfortable sleeping temperatures for each room.
Although our split system units can be set to a relatively low 16C, simply leaving them at this temperature would mean they're on pretty much all the time and consuming more power than they would be had they been off completely. The good thing about the "Climate Active" feature Sensibo has built is that you can set an "Turn on below" temperature and a corresponding "Turn off above" temperature. You can also set specific modes for fan speed, temperature target and vane movement. This is important overnight as the vanes moving is one of the more noisy components of an AC.
As I write this, the last few nights have been really cold in Kyneton - dropping to around -2C by 6am most mornings. As you can see above, the shaded red sections are where the temperature has dropped below the threshold needed to trigger the unit, then it turns off again after it reaches the target temperature (between 15.5C and 16C). Interestingly, looking at these now, it may be ultimately more efficient to set the turn off temperature slightly higher (at 16C like it is in Claire's room), versus slightly lower (at 15.5C in Ellie's room). The 16C room was powered on for less overall as it took longer to trigger the low point. Our bedroom is set colder than the kids rooms, but also cools less quickly because there's three bodies (2 adults and a dog) warming the air. It's also larger though, so potentially that's why it cools down faster.
Another small integration with Home assistant here is that I turn off the climate react at 8am, once the kids are off to school or out of their rooms for the day, but back on again at 2pm. This way if they are below threshold, they warm up in time for them to come home (and before peak time). It may make more sense for me to stagger these turn on times to be between 1pm and 2pm, so I'm not using a heap of power all at once as the units do their initial push to warm the rooms. This will mean I'm more likely to use afternoon solar being generate, without starting to draw from the grid.
Home assistant lets me integrate with my Fronius inverter, which is fantastic. In the future, I'd like to be able to trigger the mid-day dehumidify and pre-warm sessions based off whether or not solar is being generated, or perhaps how much is being used. If there's more than 3kW being exported to the grid, I can probably turn on multiple units at once, whereas if there's only 1kW being exported, I could turn them on one at a time. Ultimately though, if it's a cloudy day, I either need to decide not to pre-heat or it makes no difference if I turn them all on at once, because I'll be paying for all that grid power regardless.
Auto-turning off blow heaters
One of the smallest, and probably most impactful wins I've managed through automation has been to get use a Kasa smart switch to drive the blow heaters we have in our bathrooms. Home assistant, in conjunction with Google Home units, means that when you go to have a shower in the morning, or need to use a bathroom, a quick "Hey Google, turn on the heater" in the appropriate room turns the blow heater on. Home assistant then turns the heater off automatically after 20 minutes. This saves us from ourselves, by saving power where you may otherwise forget to turn it off and still letting us take the chill off the air when a space is in use.
It also helps because, for example, when I've finished having a shower I can leave the heater on for whatever is remaining on it's timer and have it turn on the exhaust fan and heater to dry out the bathroom and have that automatically stop using power a few minutes.
Importantly here, we used the dumb version of the Vornado heaters instead of the ones with software and a screen. This helps because anything smart that requires a button press to turn on is more difficult to automate versus a physical switch that's just "On" or "Off". So far these Vornado heaters, although they cost more to buy, seem to last longer and distribute the air more evenly throughout the room.
Some counter-intuitive thoughts
As I sit here writing this the weather is turning bad. It's 8C ad starting to rain heavily. Does it makes sense to do my laundry on a day like this even though I'm not generating much solar? Given I'm likely to use the ducting anyway, perhaps it makes make more sense to dry my laundry at the same time. I think if it was more than just me at home, this'd be the way to go as we'll need to heat multiple rooms anyway.
There are so many little issues like this that need are all opportunties for yak shaving our energy usage. Keeps things fun and interesting.
WFH vs. WFO
All up, working from home has been great for our energy efficiency. When we both worked in an office, we'd be away from home most of the day and would contribute heavily to the duck curve of power usage that plagues the grid. While we still do this, we're far more able to shift our usage and say do a load of washing in between meetings, or pack the dishwasher at lunchtime for example. This, coupled with far less commuting (80km by diesel train into the city can't be great done every day), means I suspect we're probably using less energy than we would otherwise have been.
Where to next?
Batteries / electric cars
I desperately want a battery. Especially now that tariffs have increased so significantly, it seems to make more financial sense. A battery that would have previously been uneconomically viable probably pays for itself 50-70% faster? It's time for me to get a quote. I'll tackle figuring this out in another post.
The good thing about getting a battery is also that it'll mean we're a bit more disaster resilient as well (for at least a few hours). One protip I've learnt around batteries is that often, even if the power to your house is down, the NBN still works. Only issue is that you need to be able to power your modem, so adding your modem to the battery backup circuit seems like a good way to keep a lifeline, or means of entertainment, running.
An electric car also feels like a great idea, and working out whether it makes more financial sense to get an electric car or a home battery is something I haven't done yet. Obviously electric cars cost significantly more, but they have far bigger batteries as well.
At the moment, a battery feels like the right choice for us, given that, for the most part, we generate enough solar that we could recharge a battery most days and cover our overnight usage. The hardest part of electrification is having enough spare capital to invest in the things that'll save you money longer term.
This post is about electricity, but recently I've turned my mind to storing water and reducing water use. El Niño and droughts are about to hit, and are likely to become more common with climate change. Water is also really expensive! For a family of four and an an inefficient washing machine, getting a tank might actually be the next most logical step for us, even before a battery.
Financially, buying water from the mains means you're charged both for its supply and then also discharge via sewerage (which for us is more expensive than the water purchase itself). This means you'd save twice by using tank water (both free to collect, but you're also not paying for sewage).
In the event of a drought, I'm also super keen to keep our trees alive. Without those, things just get hotter and hotter, and they're beautiful.
That's enough for now. This ended up being a super long post, but there's so much to consider and I've learnt so much over the journey so far.