Hot Water Storage
Each array is plumbed to its own 120 gallon hot water storage tank. The two
are kept separate to compare the performance of the two systems. The
outlets of each tank are then plumbed together so they can be used
together for heating and cooling of the building.
Yazaki Absorption Chiller
The Yazaki WFC SC10
provides 5 tons of cooling
capacity. These units are
currently not available for small
applications as they are more
expensive and complex that a
standard electric air
conditioning unit.
Heat Exchangers
Two heat exchangers are mounted directly beneath the furnace. The
cooling coil has the capability to remove 42,635 Btu/Hr from the air flow.
The coil is driven by chilled water from the absorption chiller at 10 gpm
and 45°F. The heating coil has the capability to provide 54,257 Btu/hr of
heat with a flow rate of 8 gpm water at 180° F.
Data Collection
A National Instruments Field Point Unit is
used to monitor temperatures and flows
throughout the system. This real-time data is
used to provide system and component
efficiencies as well as the amount of
greenhouse gases offset by the use of solar
thermal energy.
DRI plans to continue collaborative solar research in the following areas:
cost-effective flat plate solar collectors, flat plate solar collectors for
vapor-transport systems, small-scale combined heat and power (CHP)
collectors, testing of organic PV cells, concentrated solar power towers,
and solar driven thermoelectric generators..
The electricity required to run the system is drawn from the facility’s
renewable power systems. This includes: PV and wind turbines with
electrical storage in batteries and H2 which can later be combusted in an
internal combustion engine.
Located in Reno, Nevada, the DRI North campus is a prime candidate
to perform solar research. DRI has participated in both solar thermal
and solar electrical projects in recent years. Most of these solar
capabilities are now incorporated into DRI’s Renewable Energy
Experimental Facility (REEF). This includes solar thermal air collectors,
liquid/glycol collectors, and water collectors; in addition both tracking
and fixed to photovoltaic (PV) arrays. The REEF consists of a 1200 ft2
home and 600 ft2 workshop.
A practical and cost-effective method to utilize solar energy is to capture
solar radiation as heat. This energy can then be used in both heating
and cooling applications. Two types of solar thermal collectors have
been implemented into the REEF House: one roof mounted and the
other ground mounted.
Because potable water is passed through the Sunvelope collectors, this
eliminates costly components and complex heat exchange systems. The
flexibility allows for additional uses such as steam generation for
electricity production.
Fig. 1. REEF House Solar Thermal Collectors
The 200 sq. ft. array mounted
on the roof are Sunvelope
Solar collectors, made in
Sparks, NV. These collectors
utilize an “envelope” system
that allows them to expand
and contract with temperature
change. These collectors can
withstanding freezing and
boiling without the use of a
drainback system.
Fig. 2. Sunvelope Solar
Collectors
Fig. 3. REEF House HVAC System
Fig. 6. Heat exchangers and
furnace
The thermodynamic cycle of
absorption refrigeration is a
method of air conditioning that
can be driven by solar
applications. Figure 4
demonstrates how the system
operates. The principle is that a
refrigerant will absorb heat from
the conditioned space as it cools
due to evaporation.
System Control
Fig. 4. Thermodynamic Cycle
Fig. 5. Yazaki Absorption Chiller
A 200 sq. ft. array of Viessman glycol based
solar thermal collectors is ground mounted on
the south side of the house. The racking
system allows for manual adjustment from 10°-
62° The glycol based mixture heats water
through a heat exchanger mounted in a control
box.
System Configuration
Hot water is pumped from the
hot water storage tanks to
either an absportion chiller for
cooling or a heat
exchanger/coil located in the
house ductwork. A schematic
of the system is shown in
Figure 3.
The system is controlled by a thermostat,
similar to that used in any typical
residence. The thermostat is set for
heating mode and cooling mode. During
times of heating, the gas furnace is used
as a back-up.
Viessman Collectors
Sunvelope Collectors
Divicon
Controller
Expansion Tank
T T
Cooling TowerAbsorption Chiller
Expansion Tank
Drain
Expansion Tank
Drain
Chilled Water
Chilled Water Return
Water Return
Hot Water
Cooling Water
Cooling Water
T
T
T
T
T
T
T
T
To Pump (Supply)
To Pump (Supply)
Legend
Pressure Relief Valve
Manual Ball Valve
3-Way Solenoid Valve
T Thermocouple
Flow Meter
Pump
Viessman Water Tank
Sunvelope Water Tank
Check ValveOverflow Container
From Collector (Return)
From Collector (Return)
Heat Exchangers
The hot water from the solar panels is used to raise the temperature of
the refrigerant, causing it to evaporate.
Data on the system is
collected 24/7 every 5
minutes. Figure 7
shows various
temperatures over a
two day period. The
shaded regions
represent times when
the absorption chiller
was operating.
Fig. 7. Data collection from HVAC system
Fig. 8. Economizer
A custom economizer was built
for the HVAC system to provide
cooling, for times when the solar
collectors are not hot enough to
operate the absorption chiller.
The economizer draws in
outside air when the enthalpy
outside is lower than the
enthalpy inside.