Does a time switch on your geyser actually save electricity?

This is the question everyone has been asking and I too have been wondering.
I have created an “ElectricityUsageCalculator” (Excel spreadsheet) for you to calculate your usage and where you can make savings.

In fact, in the quest for the answer I have taken the long path of reducing my household’s electricity consumption and I thought that I’d share this information…

Before I get to the detail, I’d like to thank the following people/organisations/forums for sharing their valuable information:

• Talk Radio 702 Power Guide: http://www.702.co.za/power/usage_list2.asp
• “Parkhurst Post” Editor, Tim Truluck: http://www.parkhurst.org.za/post/feb08.htm
• http://energycrisis.co.za/?p=56
• Eskom’s Conserving Electricity page: http://www.eskom.co.za/live/content.php?Item_ID=274&Revision=en/0
• Eskom’s demand side management: Solar Heating: http://www.eskomdsm.co.za/swh_4_9_timer.htm
• Saving Electricity 101: http://michaelbluejay.com/electricity/howmuch.html

Why not pay these sites a visit?

Cutting to the chase:

OK, so some of you don’t really want to know how I got to the “findings”, you just want to know if turning your geyser off and on really saves you Rands, so here goes:

*) if you have a solar panels, then yes - installing a time switch on your geyser will definitely save you money (without time switch: electricity and solar will heat up the cold water, and so electricity will be used. With time switch: only solar will be used to heat up the cold water; electricity will kick in if the time switch is set to use electricity for critical time periods. See here for more details: http://www.eskomdsm.co.za/swh_4_9_timer.htm

*) if you don’t have solar panels, then you’ll probably not save a lot of money by installing a time switch: Niel says (see comment on 6^th February 2008 @ 10h08: http://energycrisis.co.za/?p=56) that you’ll “only save electricity if you leave your geyser off for 2.5 days”; and “you can’t save electricity by switching a heater on and off, as the amount of energy required to keep it at a certain temperature for a given time and to heat it up again after that given time is the same.”
Again, referring to Niel's comment February 12th, 2008 at 1:01 pm: <> "...my geyser was on for 46 minutes over a 24hr period or basically for 1 minute 55 sec every hour..." <>

….rather insulate your geyser (using a geyser blanket) and hot water pipes to reduce the heat loss.

….but if the time switch is set to turn the geyser off during peak times, then you will help Eskom to reduce the peak loads and perhaps reduce the need to load-shedding…. But isn’t Eskom installing those ripple switches for this? {Yeah, but until then…. best we do our bit to make our lives easier!}

If you do want to save money try these steps (in the order listed):

*) turn down the temperature setting on your thermostat (mine is set to 35^oC) – you know when it’s set right by the amount of cold water that you need to mix when you’re having a shower…. If you’re mixing a lot of cold water, then you know that your thermostat is set too high – you need to turn it down (colder), until you are mixing little or no cold water for your shower.

*) use less hot water (ie. Install a low‑flow shower head [I have an RST low flow one], and shower quickly) to save electricity – the less cold water that your geyser needs to heat up, the less electricity is used.

*) use the ‘Electricity Usage Calculator’ to see where you ‘spend’ your electricity.

Download from here: ElectricityUsageCalculator02.xls

I was amazed to see that my main “culprit” was not my geyser, but in fact my swimming pool pump! [thanks Tim Truluck for pointing this out to me!]

Don't edit the shaded cells....

Step 1) In the worksheet ‘PerHourCosts’: check the ratings (W) listed [column D] and adjust to your appliances' ratings;

(Note which appliance is the most costly to run per hour)

Step 2) In the worksheet ‘UsageCosts’: fill in the 'hours used per item per month' [column D];

(Note: 'Cost per item per month' - the high cost items is where you can save the most)

*) Lastly, use solar power to heat your geyser: install solar panels. If you are building a new house or if you replace your geyser, then install solar panels and a time switch.

Detailed explanations:

*) Electricity is used by a geyser each time the temperature of the water goes below the thermostat’s trigger temperature.

*) Refer to the worksheet ‘GeyserThermostat’ for the following explanations:

*) Assuming the water in the geyser is cold to start with, and the thermostat is set at 60^oC, then the thermostat will turn on and allow electricity to flow to the geyser’s element which heats up the water [this costs about R2.30 per hour]. After about 65 minutes, the water temperature will be above 60^oC and the thermostat will turn off and no electricity will be used.

*) When someone in the household decides to take a shower, the hot water exits the geyser and cold water replaces this hot water which forces the temperature to below the thermostat’s trigger temperature of 60^oC. At this point, electricity will again be used to heat up the water to 60^oC at which point the thermostat turns off again.

So, as more hot water is used, more electricity is used.

*) Heat loss will be small on modern (or geyser‑blanket clad) geysers and piping, but the lower the thermostat temperature, the lower the losses, and the lower the electricity that is used to get the water to the thermostat temperature. Comment from Dave on http://energycrisis.co.za/?p=56: “I turned my geyser down from 60^oC to 50^oC and saved 20% on my bill”

*) A solar‑only geyser will heat up the water more slowly (note: the thermostat plays no role in limiting the solar‑only upper temperature)

*) Installing a time switch in a solar installation will: 1) ensure that electricity is not used on a sunny day (i.e. on a sunny day you would rather have a slower heating up of the water by the sun, rather than use electricity and solar to heat up the water faster); 2) ensure that electricity is used so as to guarantee that there is hot water early in the morning and, in late afternoon on cold/cloudy days.

How do I find out how much electricity something uses?

Adapted from “Saving Electricity 101”: http://michaelbluejay.com/electricity/howmuch.html

Look at the label - nearly everything you can plug into the wall has a label that says how much electricity it uses.

If the label only gives the number of Amps and not the number of Watts, then just multiply the Amps by 220 to get the number of Watts. (Amps x Volts = Watts. So a hot plate that uses 3 amps uses 3 x 220 = 660 Watts.

Note that if a device is powered by a transformer (one of those great big plugs), then the transformer has converted the electricity from AC to DC, so you need to multiply by the DC voltage, not the AC voltage of 220. For example, if the device says "INPUT 9V, 0.5A", then that's 9 volts x 0.5 amps = 4.5 Watts.

Another tip:

*) Remember to turn off your ‘plug’ circuit breakers when you’re in “load-shedding” mode – this will ensure that your appliances are not connected to Eskom when power is turned on again – remember, when power is turned on again, there is usually a surge (over 220V) which could damage your appliances. Leave a light turned on, so that you know when power has returned, then turn your ‘plug’ circuit breaker back on again.

An alternative would be to purchase surge protectors for your most expensive/vital appliances.

Update on 16June2010:

Watch out or, at least, be aware: #WTF Geyser's element has just blown <3 years after installation... 5 year geyser warranty, but only 3 months on the element! #FFS #RipOff

http://www.xstream.co.za/warranty.htm