14 June 2002
c. Temperature Differences Across the DHW Heat Exchanger.
Temperatures were measured by exposed junction type-T thermocouples taped to the
outside of the copper tubing and insulated to minimize the influence of the outside air
temperature. Recorded temperature differences across the DHW heat exchanger for
the months of May, June, and July can be seen in Figures G-15, G-16, and G-17.
d. Temperature Responses. Temperature responses recorded on May 8,
June 17, and July 15 can be seen in Figures G-18, G-19, and G-20 respectively. Note
how the fluid temperature coming from the array in May reached about 65 degrees C
(149 degrees F) but in June and July it reaches 120 degrees C (248 degrees F). The
controller for the whole system is programmed to shut down the re-circulating pumps
when the water in the DHW storage tanks reaches 54 degrees C (130 degrees F). The
demand for hot water was low enough in these months that the system controller shut
the re-circulation pumps off, which in turn caused the fluid temperatures in the array to
e. BTU's Measurements. An energy monitor was installed on the DHW system
inside Building 80306. The monitor was connected to a paddle wheel flowmeter and
two platinum resistance thermometer (PRT) temperature probes. The temperature
probes were used to measure the temperature of the solar hot water system's supply
and return water. Recorded temperature differences between the supply and return for
the months of May, June, and July can be seen in Figures G-21, G-22, and G-23.
(1) Figure G-24 and Figure G-25 presents the energy provided by the solar
hot water system to Building 80306 as well as the total water usage for each month.
The leftmost column for each month shows the calculated energy (BTUs or Joule)
delivered at 10-second intervals. The middle column for each month shows the
calculated energy delivered using the average 10-second reading over a 10-minute
period. The rightmost column shows the total water usage for Building 80306 during
each month. As seen from the figure, the two calculated energy columns are almost
identical. This indicates that hot water usage for Building 80306 was not in short spurts
or has sudden changes. Also note from the figure the dramatic decrease of energy and
hot water being delivered from May to June. The drop off in delivered energy and hot
water can be accounted for by the fluctuating occupancy of the facility. During June
and July, Building 80306 was not fully occupied.
(2) The energy monitor used to record the measurements shown in Figure
G-24 and Figure G-25 was replaced with a new, more accurate monitor in September
1997. Data from this new monitor has been continuously collected since it was installed
in September and is shown in Figure G-26 and Figure G-27. As seen in the figure, the
solar hot water system supplied a peak of 25.5 MBTU's (26,800 MJ) in March of 1998
(this also corresponds with the highest monthly water usage). Figure G-26 and Figure
G-27 also show gas usage for Building 80306 since September 1997. The gas readings
include the amount of gas used for both the DHW gas heater and the clothes dryers.
Heat is supplied to Building 80306 from a central plant. Note how for March the water
usage almost doubled from February. The energy delivered by the solar hot water
system also almost doubled but the amount of gas used only increased by 15%. This