GeyserWise . . . . . . not saving in Power Save Mode

As far as I’m concerned, my GeyserWise thermostat timer paid for itself within a few weeks. Then it started costing me money.

The GeyserWise is an electronic device that replaces both a timer and the thermostat on an electric geyser element. As I have stated before on this website, a timer is an essential part of a hot-water solar system. The GeyserWise would appear to be the ultimate geyser timer, allowing the user to set multiple programs to turn the geyser element on and off, to see the temperature inside the tank, and to adjust the thermostat setting from a comfortable position several meters away from the geyser itself. No more crawling into the roof space with a headlamp and screwdriver.

I paid R1300 for my GeyserWise, including installation by an electrician recommended by the manufacturer. Here’s how it paid for itself so quickly. Monitoring the temperature inside my tanks, I started noticing that the water would cool off by a few degrees in the late afternoon every day, even though no one was using hot water. Worse yet, I could see that the pump for the solar panels was running for an hour or more as the water temperature fell. The solar panels were literally cooling down my water!

With a quick phone call to my solar installer, SolarHeat Exchangers, the problem was solved. My installer explained to me how I could easily check the temperature differential controller that decides when to pump heated glycol from the panels to the geyser tanks. The controller is designed to switch on the pump when the panels are sufficiently hotter than the water in the tanks. Mine was set to activate the pump when the temperature difference reached 3 degrees Celsius, a standard setting for one tank located close to the panels. But I have two tanks, a warm tank to feed a hot tank in series, and my panels are quite far from those two geysers. In the late afternoon, the panels were still 3 degrees hotter than my warm tank, but by the time the glycol reached the geysers, it was cooling off the hot tank. I turned the controller setting up to 9 degrees, so that the pump only runs when the panels are much hotter than the water in the tanks. My water has been a few degrees hotter ever since.

That’s when the GeyserWise started costing me money. Most people are content to let the electrical element in the solar geysers top-up the temperature each day. They are happy to know that the sun is at least helping to heat their water and can confidently run a hot bath at any time. I’m a bit more extreme than that. Nine months a year, I kept the electricity to the geysers switched off entirely, even though we suffered the odd lukewarm bath. The GeyserWise has what appeared to be a perfect setting for a geyser miser like me. In Power Save Mode, “only the temperature display will be on,” the manual assured me. With my water hotter than ever, thanks to my sleuthing with GeyserWise, I began routinely using the Power Save Mode so that I could keep an eye on the temperature in the tanks without resorting to electrical backup. Or so I thought.

For months I scratched my head, wondering why the temperature in the tanks would rise in the night. I assumed some sort of mysterious thermal mixing was taking place. I also wondered why I unaccountably struggled to keep my electricity consumption below 16 kilowatt hours a day. Then I noticed that if I switched off the power to the geysers at the wall, my daily consumption fell by about 3 kWh. It was time to call GeyserWise.

David Hartzenberg, who handles technical support for GeyserWise, explained that I had been misled by the manual. The Power Save Mode does not change any of the thermostat or timer settings, it merely switches off the rest of the LEDs in the display. Hartzenberg admitted that this saves a miniscule fraction of a watt. To monitor the geyser temperatures while feeling safe that the element will not switch on, he recommended that I rather set the GeyserWise to heat the water between 3 pm and 5 pm, with a low thermostat setting such as 30 degrees. Since the solar-heated water virtually never gets that cool in summer, I can monitor the temperature without ever switching on the electric element. Now I am in a mode that truly saves power.

Of course a GeyserWise doesn’t have to be used in conjunction with solar panels. The original idea behind the device was to prevent ordinary electric geysers from heating up water during the day while the householders are at work and school or at night while they are asleep. A study of GeyserWise by the Cape Peninsula University of Technology found that by heating water only in the hours immediately before the family is likely to use hot water, the Geyserwise saves about 10 percent on electrical consumption by the geyser. This could save a typical suburban family a couple hundred rand a year.

So do I recommend the GeyserWise? I’m torn. The confusing manual alone is probably not reason enough to avoid buying one. GeyserWise has already put a somewhat better manual on its website, though they have not cleared up the Power Save Mode muddle. I will put clear instructions including my own recommended GeyserWise settings for solar panels on GreenerHouse at a later date.

I have, however, heard negative reports in the industry. Electrician Ian Sands says that he installed GeyserWise in 40 homes before giving up, because 30 percent of them were causing troubles. Dylan Tudor Jones of Solar Heat Exchangers recommends that a simple geyser timer costing a few hundred rands accomplishes much of what a GeyserWise does with far less complication. Hartzenberg at GeyserWise counters that the error codes that typically lead to complaints are indications that something is wrong with the geyser, not the GeyserWise.

In the end, I believe it boils down to personality. If you don’t care to know the water temperature, and don’t want to tinker with thermostats and multiple timer settings to minimize electricity consumption, you probably just need an ordinary geyser timer. If, like me, you want to squeeze every last kilowatt, the GeyserWise is very handy. Being able to lower the thermostat in summer and raise it in winter with the touch of a button and then fine tune it according to your needs is an easy way to make significant savings. Checking the water temperature at a glance not only saves me kilowatts hours and rands, but may also have saved my marriage. Each night before bedtime, I now can make sure that a cold bath won’t put the chill on romance.

When I first wrote on GreenerHouse about dishwashers, I lamented that I could not find one with a hot-water inlet. For most of the year, I have an excess of solar-heated hot water sitting in tanks, so it is a waste for my dishwasher to be electrically heating cold water. At the time, I had been misinformed by a Bosch technical expert that the inlet to my dishwasher could handle a maximum of 40 degrees. Like an idiot, I hadn’t read the manual, which says that the inlet can take up to 60-degree water.

Water heated by flat-panel solar collectors does not tend to rise much above 60 degrees, and my kitchen is far—too far—from my water tanks to ever get to 60 degrees at the tap, according to my thermometer. (Vacuum-tube panels do often produce much hotter water, and may require a thermostatic mixer to keep temperatures at safe levels.)

So I recently asked my plumber to connect the hot water to my dishwasher. My hypothesis was that the thermostat inside the dishwasher would switch off the heating element more quickly with warm water entering the machine. Using a cold-water feed, this Bosch, A-rated model uses approximately 1 kWh per load at the 35 degree “Quick Wash” setting. After connecting the hot water, I recalculated the energy consumption, using the technique outlined here. It has fallen to 0.7 kWh per wash. Over the course of a year, this simple change should save about 100 kWh preventing some 100 kilograms of carbon dioxide from being released into the atmosphere.

If my dishwasher were located closer to the hot water, the savings would be far greater. In designing a new house, ideally the north-facing roof, solar panels, hot-water tanks, bathrooms and kitchen should all be as close as possible. If this is not possible, small-diameter Pex pipes can help overcome heat loss over long distances. (Combining Pex pipes and vacuum-tube solar collectors is asking for a meltdown, however.)

I compensate by running the hot water in the sink, usually while washing pots and pans, immediately before switching on the dishwasher. That way the water enters the machine hot for the wash cycle, though only slightly warm after the copper pipes have cooled the water for the two rinse cycles. One day I will try insulating the pipes and see if I get even better results. In the winter, when the sun does not always provide enough hot water, I will try to run the dishwasher in the late morning, so as not to deplete the evening supply of hot water.

Coincidentally, just days after my plumber had made the connection and before I had a chance to measure my results or write about it, a GreenerHouse reader published a comment here, reporting how pleased he was with his hot-water connection to his dishwasher. All green minds think alike.