As I said in the last post, the primary benefit of running the DWHR performance test was the discovery that it wasn’t operating as intended. It gave me a chance to fix the problem and have the heat exchange and heat recovery process run at its full potential, which I measured at 46.7%.
That in turn should help me save some money, which is important to make this investment pay off. There is a lot of copper in the DWHR, and it doesn’t come cheap. We bought ours for $617.00 a few years back.
To sweeten the investment, Renewability provides an energy savings calculator on their website, to give the consumer an idea what level of savings could be expected.
Our DWHR (the R2-60 PowerPipe) serves the first floor and second floor bathroom showers. I assumed an average occupancy of 3 people per apartment, 0.75 showers per person per day and a shower time of five minutes. According to the energy savings calculator, we could expect annual savings of
- 388,605 Btu (or 4.1 gigajoules),
which would translate into
If I increase the shower time to 10 minutes, the expected annual savings increase to
- 767,732 Btu (or 8.1 gigajoules),
which would translate into
- $132.96 savings per year.
I guess the savings will lie somewhere in between the five and 10 minute shower time scenarios, and so will be the payback time for the DWHR, which would fall somewhere between four and a half to nine years.
That “M” word!
Using the calculator is not as straight forward as you may think – as I found out. First, it appeared to be down quite a lot, displaying an error message. This may just be a temporary issue, or so I hope.
Secondly, using the calculator, I was reminded that it is us (or should I say US) against the rest of the world. I think we must be the only culture left that doesn’t use the metric system. Canada does use the metric system (bless the Canadians!), and Renewability, the manufacturer of the DWHR, is a Canadian company.
The use of the metric system becomes relevant in the energy calculator if your fuel type is natural gas. The input field ‘Cost of Fuel’ uses the unit $/cubic meters natural gas – and not therms! A subtle detail that makes a difference in the calculator output.
How do you determine the cost of fuel?
And I am not talking about unit conversion – yet. Should I just use the cost per therm and ignore all the delivery charges and other add-ons?
I opted for what would I call the true cost. I added up the total volume of cubic feet of natural gas delivered over the past 12 months and converted it into cubic meters. I also added up the bill totals for the past 12 months and divided it by the total cubic meter volume. That gave me an average fuel cost of $0.55 per cubic meter of natural gas.
The $0.55 fuel cost is a snapshot. It is on a sliding scale depending on the occupancy of the building and natural gas prices.
I also have to take the calculator output at face value. I have not cross-checked the results through my own calculations. The fact that the advertised effectiveness of the DWHR was right on par with my own test results gives me some confidence into the energy savings calculator results.
DWHR performance test – good data
Troubleshooting test results
Test results to dream of
That heat is mine, and I plan to keep it!