Back to Basics: Boiling the Kettle

How much energy does it take to boil the kettle? Is it more than I need to use?

Some time ago I realised that I almost always overfill the kettle, and I have been working at reducing how much water I put in. It took a while to get the hang of it, but I can now say we are committed to putting in only as much water as we intend to use. As my mum and dad are visiting from Victoria for a couple of weeks, our kettle is working extra hard and it seemed timely to publish this commitment.

This is a simple post about a simple action in tune with our original intention to take up one additional act towards sustainable living per month. 

Initial Time: zero - but it did take many months to change old habits. 

Like my habit of filling and boiling the kettle half an hour before guests arrived, so they wouldn't have to wait so long for their cuppas. This then required reboiling the kettle when they arrived and often I had more hot water than I needed because I didn't know in advance how many cuppas I would be making. I can't think of a guest to our house who would mind waiting a few extra minutes for their hot drinks.

Or the practice of someone in this house (who shall remain un-named) of boiling the kettle then an hour later remembering the cuppas have not been made so reboiling the kettle... and perhaps  remembering this or the next time to actually do something with the water...

Initial Cost: zero - a cost saving (see below)

Ongoing time or cost commitment: zero

Impact: When I fill our kettle I am generally boiling around 1.25L more water than I need. It takes 430.5kJ to heat 1.25kg of water from 18°C (ambient temperature) to 100°C (boiling). This is equivalent of approximately 120Wh. 

To put that in perspective, every time I boil a full kettle to make one or two cuppas, the excess energy I am using is equivalent to leaving two sixty Watt light globes on for an hour, or to having our energy-saver 20 Watt kitchen light on for six hours.

If I boil the kettle full four times a day, in a year I would have used 174.5 kWh of electricity doing nothing at all - boiling water I don't need. Our Perth electricity company currently charges 26 cents per kWh (unit) and we have opted for a natural power premium of an extra 5 cents per unit. This means our commitment to only boil the water we need is saving us $54 per year (plus GST - total close to $60).

[for those interested in formulas: 

change in temperature (ΔT) x mass (M) x heat capacity of water (C), 

where ΔT=82°C M=1.25kg C=4.2kJ/kg°C = 430.5kJ

1 kWh = 3.6MJ

0.4305 / 3.6 = 0.1195kWh = 120Wh

0.1195kWh x 4 boils per day x 365 days = 174.47 kWh]

Thanks Tyson for knowing the formulas... I'll have a cuppa next time you're boiling...

What to do when the hottest week on record is forecast for your city

When the forecast showed Christmas day as the first in a run of seven days close to 40°C, Perth's hottest week on record, we knew it would test our commitment to sustainable living to its edges. The temptation was to pour water on the garden, crank the airconditioner and stay inside (possibly in front of some energy-consuming electronic entertainment). Here are a few things we did to ride out the week of heat without maximising our environmental footprint.

- Wore wet flannels to feel cooler. When I lived in an uninsulated unairconditioned fibro house I used to freeze wet tea towels in a U-shape and wear them around my neck. Now if I am reaching that point I consider we are past the 'bearable' test and its time to turn on the aircon.

- Sent Eva to bed with a squashy ice pack.

- Breastfed baby twice as often... as if the heat wasn't making me tired enough already!

- Kept the fridge as full as possible, filling empty spaces with blocks of ice or cold water, to improve thermal mass by reducing the amount of air to be kept cool. Air is hard to keep cool because it escapes whenever the fridge or freezer door is opened. 

- Shaded everything! In addition to the summer-long emplacements we added some temporary foam rubber mats along the kitchen & rear toilet windows and a tarpaulin over the clothesline. The foam rubber mats make a huge difference. The glass inside was noticeably cooler behind the mats, even before the sun was on the window, and even the cranky thermometer registered about 4 degrees difference between the covered and uncovered glass.

- Washed every day to ensure there was enough grey water for the garden. We always run the washing machine with a full load, so I worked my way through 'sometimes' items (towels, sheets, bathmats etc) to ensure the garden got water every day without having to give it pure drinking water from the tap. On a couple of the hottest days I did two loads and gave the lawn a good soak.

- Played outside in the mornings for as long as possible (for exercise, fresh air and to prevent against cabin fever). Did quiet indoor activities through the worst of the heat (lego, trains, playdough, craft, hide & seek, tea-sets, dolls & teddies, etc). Read a lot of books.

- Had cold or nearly cold showers, cool baths, and used the paddle pool sparingly (and put the water onto the garden when shower/ bath/ play was over).

- Were disciplined about the water-catching bowl in the kitchen sink, and got it out onto the courtyard pots any time it was full to help the plants through the worst of the heat.

- Ran fans rather than the airconditioner for as long as this was bearable. We turned on the aircon on four of the seven hot days - on three of those days for only about three hours. On day three, when we used it first, we set it at 28°C. On day five, when it came on again, the walls of our house had soaked up more heat and we dropped the aircon to 26°C. This is easily enough to cool our living spaces. (Due to the location of the air conditioner unit, even running it like a fridge would not really cool our bedrooms).

- At night, opened the house up to cool as much as possible before morning. We ran the extractor fans to help remove the day's heat and placed pedestal fans in the eastern windows (the overnight direction of cool air if any is coming) to help draw in the breeze.

- Didn't cook (or barely cooked). Christmas leftovers helped with this. We also reheated some frozen meals in the microwave. When we used the toastie maker we then put it outside to cool, so that its heat was not added to the inside temperature. We definitely did not turn on the oven, and only used the stove for about an hour in total all week.

- Went out to places that were cooler (eg the beach, the shady playground beside the lake) or where airconditioning would already be running for other people (Tyson's work, grandparents' house, public facilities). This is not about letting others carry our footprint, but about maximising the number of people each aircon serves, thereby minimising the total number of airconditioners running. On New Year's Eve it was our turn to run the airconditioner on behalf of a group of families. We ran it for 13 hours, but for much of that time had members of up to seven other households sharing it with us.

- Did not increase screen time. We don't have a TV at all. Tyson & I watch a little I-view but Eva is allowed only a very occasional episode of Playschool under extreme circumstances (like the week she was stuck home with hand foot & mouth disease recently). Although I had Playschool in mind as an 'if all else fails' emergency activity for the heat we didn't need to go there - perhaps because the room with the computer is not the coolest room in the house.

Despite being over 42°C on New Year's Eve, with the road still hot under our bare feet at midnight as we watched fireworks in 30°C heat with no breeze, not all the predicted maximums were reached. The average maximum temperature of 39.4°C made it only the hottest week in 34 years, the third hottest week in 116 years of records, and the hottest December week on record, NOT the hottest week ever. Lucky us, eh?! Even though it was only below 25°C for a handful of hours all week, in some early mornings, and didn't get below 20°C at all...

None of these actions had any initial cost, and time commitments were very small (a matter of a few minutes here and there).  

The impact is difficult to measure in any precise manner. Certainly if we had not used passive cooling measures we would have run the airconditioner a lot more in the past week. Its hard to say exactly how much energy this would have meant, as it depends on things like the temperature outside, the temperature the aircon is set to, and how much we would actually have turned it on, but the aircon uses (roughly) between 1.5 and 2kWh (units of energy) per hour. Perhaps as much as 100kWh was saved by limiting our aircon use. If we had run it 24-7 for the week it could have used between 252 and 336 kWh in total.

More importantly, we did not significantly increase our demand for power through a peak period of demand. Demand in peak periods wastes energy all year, as the whole system needs to be built for extremes rather than averages. Minimising peak usage has more impact than minimising average usage. 

I'm quite pleased with how well we did. One more day and I think I would have collapsed. But then, if one more day had been forecast I would have paced myself for eight days as I paced myself for seven this time. Tyson thinks any of our more usual three or four day heat waves for the rest of summer will seem so easy to manage by comparison that we may not turn the aircon on again all season. I have my doubts. I've booked a holiday to southern Victoria in a few weeks to visit my parents rather than ride out the whole summer here - thereby, in two cross-country flights, practically wiping out any footprint gains we make by reducing our domestic power usage here. Ah well. Its about small steps.

Just when you think you can't shade anymore...

When I wrote in December about our summer shading system I thought we had shaded everything we could reasonably manage. But as it got hotter we found more exposed areas that could be protected and added:

additional dense (90% block-out) shade cloth to patch a gap in the rear (southwest) courtyard shading,

 

on very hot days, a towel inside the (northeast) bathroom window, which has no eaves,

on very hot days, an old painting canvas inside the (southwest) laundry glass sliding doors, which get blasted with afternoon sun,

 an old woollen wall hanging on the southwest wall outside Eva's bedroom, and

three towels left on the clothesline all summer along the northwest living area wall.

These also make a good cubby.

Initial Time: Shade cloth: fifteen minutes to bend hooks and hang the cloth; wall hanging:five minutes to put a hook in; towels: 30 seconds each to hang; paint canvas: 30 seconds to balance in place on the grey water bin.

Initial Cost:$20 for shade cloth, zero for towels, paint canvas or wall hanging (which was being thrown out by a family member)

Ongoing time or cost commitment: One or two minutes every week or two to readjust the rear shadecloth as it slips a bit in windy weather; 30 seconds each on hot days to put up the inside towel and paint canvas; probably about ten minutes at the end of summer to pack away for cooler weather.

Impact:A southwest facing vertical surface in Perth in summer receives approximately 3kWh of energy per square metre per day. If the surface is unshaded transparent glass, almost all this energy gets inside the house as heat. The additional shading to our rear courtyard gives 90% shading to about 3 square metres of glass, reducing the amount of heat entering our living area in summer by approximately 8.1 kWh per day. We have a 300% efficient reverse cycle air conditioner in the living area which would use 2.7 kWh of energy to remove 8.1 kWh of heat.So, by shading instead of turning on the airconditioner most days, we are saving 2.7 units of electricity per hot day just with this one area of shade cloth. Put another way, we start to get ahead of the $20 spent on shade cloth on the 27th day of not turning on the aircon. (Thanks Tyson for knowing the numbers!)

In less precise terms, I estimate that this summer it has generally been the third day in any heat wave before we turn on the airconditioner, and last summer I think it was more often the second day. I consider a heat wave to be when the temperature stays at the mid thirties or higher for more than one day. Our airconditioner rarely runs on days with temperatures up to the low thirties (celsius!).

Calculations for the towels and wool hanging shading wall areas, and the paint canvas inside vertical blinds, are more difficult, but we notice that these rooms heat up slower. (In terms of impact, one woolen wall hanging also has a new purpose in life and has been saved from landfill, at least for a while.

Our recent power bill for 22 Dec to 24 Feb shows an average electricity usage of 8 units a day (530 units total), a very very small reduction on the same period last year (10 units less over two months). Most of the past year our average usage has been around 6 units a day, so summer is still presenting the biggest challenges for reducing electricity use at our house. It was the fourth hottest summer in Perth ever recorded (since 1897) and I was going to excuse our tiny reduction by pointing to this fact - until I discovered two of the other three hottest summers were 2009-2010 and 2010-2011. (Its hard to deny climate change when three of the four hottest summers here in the last 115 years were the last three consecutive years... the other was 1997-98). So my alternate excuse for our electricity usage not reducing compared with last summer is that this year I am pregnant and feel hot quicker!

To put our usage in some perspective, however, Synergy (our local electricity supplier) estimates the average household electricity use in WA's southwest grid is 6250 kWh per year (over 17 units per day). Our household's 2011 usage was 2452 kWh (6.7 units per day). We are living a perfectly comfortable existence on that amount of energy.

Cold Water Washing

When we bought cloth nappies we considered the instructions about how to wash them somewhat over the top, and scaled our practice down a great deal. However, I did sufficiently listen to their advice to 'wash in very hot water' to set the washing machine temperature to about 35 degrees (Celsius!) - less than half the recommended temperature, but definitely not cold. Recently I decided to try washing the nappies on cold for a while and see if it made any difference. Results: no difference whatsoever to the quality of wash. (Tyson now tells me he has always washed on cold and had no idea I was using hot water) Our washing machine is now permanently set to cold.

Initial Time: Fractions of a second to turn the dial. Several weeks of assessing whether the nappies were really coming clean, but that was testing rather than time taken to make the change.

Initial Cost: Zero.

Ongoing time or cost commitment: Zero.

Impact:  We estimate this is saving about 1.42 units of energy per day (1.42kWh). That's a total of 517 units per year, or 513 kg of carbon dioxide.

This calculation is based on our estimate that a wash uses about 70L, which is about how much we could capture last summer when we were bucketing from the washing machine, if we emptied buckets between the wash and rinse cycles. It takes 1 unit of energy to heat 20L of water by 42 degrees, and water generally starts at around 18 degrees. As cloth nappy users, we wash pretty much every day. 

The information we could find on either the washing machine itself or the web claims our Whirlpool WF665 front loader uses only 307kWh per year to heat an undefined amount of water to 'warm' every day (presumably the hottest setting) and suggests the machine uses somewhere between 55 and 60 L per wash, varying depending on the size of the wash load. Our experience of catching the water, and the physics of heating water, suggest these claims are not accurate. 

It is not possible to calculate accurately how much we are saving if the 307kWh claim is true, as we can't tell how much of that energy is for heating the water and how much for operating the machine. However, newer machines that Tyson has seen through his energy auditing work show energy use for both cold and hot washes, and he says that generally hot washing is rated as using 5-8 times the energy of cold washing. At five times the energy, based on 307kWh per year, changing from hot to cold would be saving us 245.6 units per year (244kg of CO2). Possibly a little less as we were not previously using the highest possible temperature setting.

Its not about the money, but just to give an idea: that's between $60.10 (based on Whirlpool's figures) and $126.51 (our figures) per year at the current cost of electricity.