Thermal energy storage makes it easy to be green

Years ago, consumers began cutting their home energy usage by installing compact fluorescent light bulbs, buying Energy Star appliances, upgrading to high-efficiency furnaces and turning down the heat. Today, there are even better options, but an interesting thing happened when consumers started reducing their energy consumption. Utilities changed how they billed us, with fixed fees overwhelming any savings from energy efficiency.

Does it still make sense to even try to reduce your energy consumption? Many people can’t afford cost-of-living increases, let alone expensive energy improvement projects. Those who can afford to invest in climate solutions often balk at the upfront costs and the 10- to 20-year payback period.

Big-ticket items like solar panels, triple-pane windows, heat pumps and electric vehicles are out of reach for many consumers, but there is a new technology that could catch on as a practical solution to reducing natural gas consumption and it simply requires replacing your hot water tank when it expires.

Scotland’s Sunamp Ltd. has developed a residential thermal storage water heater that acts like an on-demand hot water system and is half the size of the hot water tank it replaces. Sunamp accomplishes this using a phase change material (PCM) as the heat storage medium, instead of keeping the water hot in a big tank.

When the PCM is heated to a threshold, it changes phase and releases even more heat energy. The PCM can be heated with an internal electric heater or with hot fluid from a heat pump that circulates through a heat exchanger inside the thermal storage unit. The material is able to store up to four times more heat than an equivalent volume of water.

When cold water is run through a second heat exchanger, the PCM heats the water to a temperature that can be used for showers, laundry and washing dishes. You can further improve overall efficiency by adding a heat pump to the system because you can get two to three times more heat out for the amount of electricity you put in.

Once charged, the thermal storage unit will stay hot for days because it has much less heat loss than a hot water tank. If your home has solar panels, the unit can be charged up during daylight hours and provide hot water at any time of day.

In my home, I have a dual-function, natural gas hot water heater that has an internal heat exchanger, which circulates fluid through our basement’s in-floor heating pipes. The cost when it was installed in 2013 was $3,570, including GST. Sunamp estimates a comparable thermal storage system would cost about $4,000, not including installation.

A Sunamp Thermino 40e thermal battery is roughly equivalent to my 55-gallon hot water tank and should consume about 1,800 kWh of electricity per year when charged by its electric heater (no heat pump). This estimate is based on our past energy consumption for hot water and in-floor heating.

Our existing hot water tank consumes an average of six gigajoules (GJ) of natural gas each month, for two people and a dog that rarely takes a shower. The monthly consumption can be as low as two GJ in the summer when the in-floor heating is barely running. Based on my estimate, the Thermino 40e will have just under half the annual energy cost of the natural gas water tank, saving us about $200 a year.

The big benefit comes when I look at the reduction in greenhouse gas (GHG) emissions. According to Fortis Inc., a GJ of natural gas is about 25.5 m³ under normal conditions, which puts our hot water heater’s annual emissions at 3,600 kilograms of CO2 based on the natural gas CO2 emissions factor for Alberta.

The Thermino will cause indirect GHG emissions of 1,150 kilograms of CO2 equivalent per year, based on Alberta’s electricity consumption intensity value. This estimate doesn’t account for the electricity generated from our solar panels, but it’s still a third of the emissions from our natural gas water heater.

Over a 20-year period, this amounts to a reduction of nearly 50 tonnes of GHG emissions, which is the same amount of GHG emissions from driving a Honda Accord over 300,000 kilometres. In provinces like Manitoba or Quebec, where electricity generation is primarily from hydro, switching to an electric thermal storage system will reduce emissions by an even greater amount.

The cost-benefit of switching from a natural gas water heater to a thermal storage system will vary based on your hot water consumption. With increasing natural gas costs and a carbon tax headed towards $170 a tonne, the economics will get better with time. However, with all the fixed charges on your bill, it may seem like you’re not saving much.

In the end, you’ll have to decide if significantly reducing GHG emissions is an important goal for you and your family. The latest report from a panel of United Nations scientists warns that our choices in the next decade will have impacts for thousands of years: “Climate change is a threat to human well-being and planetary health (very high confidence). There is a rapidly closing window of opportunity to secure a livable and sustainable future for all (very high confidence).”

Rob Miller is a retired systems engineer, formerly with General Dynamics Canada, who now volunteers with the Calgary Climate Hub and writes on behalf of Eco-Elders for Climate Action.