In cold northern climates, such as Minnesota, an IWH or CIWH heat exchanger could be damaged if standing water were allowed to freeze inside the unit.
At sites 3 and 7 where no StWH was installed, an average input output relationship from the eight StWH sites was used together with the hot-water energy output at sites 3 and 7 to compute the estimated StWH energy use and corresponding IWH and CIWH savings.
Figure 6 shows the relationship found between electrical consumption and outdoor temperature for the IWH at Site 6, where the freeze protection was never activated.
1) (1) kBtu/day (W) Site IWH CIWH StWh IWH CIWH StWH StWH to to IWH CIWH 1 83.
Hoeschele and Springer's (2008) field testing, based on a total of only 48 days of data for two water heaters (one StWH and one IWH), showed a significant difference between field performance and EF and, perhaps more important, indicated that the difference in performance between StWHs and IWHs might not be accurately captured by the EF test.
There are also outstanding questions about qualitative aspects of IWH performance, such as increased time required for the water heater to produce hot water, minimum flow rate required to activate the burner, and "cold water sandwiches," which occur when hot water remains in the pipes from a previous draw when a new draw is initiated.
Annual Energy Costs Annual Energy Costs, (1) $ Savings, $ (%) Site StWh IWH CIWH StWH to IWH StWh to CIWH 1 $ 364.
One respondent would not buy either an IWH or a CIWH because of the increased delay time.
Specifically, StWH field efficiencies fell about 19% below their EF, while IWH and CIWH efficiencies were only about 10% below their EFs.
Paul metro area contractors with IWH and CIWH installation experience were conducted to estimate the installed costs of water heaters.
Real-world IWH efficiency averaged 10% less than EF, with a range of 7% to 14%.