Pentagon Solar Heating, Air Conditioning, Lighting, and Power System
October 2004
Produced by:
American Solar, Inc.
Annandale, VA 22003
www.americansolar.com
Foreword
This document is the final deliverable under Pentagon contract MDA946-03-C-0016.
The contract was initiated in March 2003 with funding from the Energy Conservation Investment Program.
The purpose of the contract was to demonstrate several “first ever” applications of solar energy, while reducing the energy use of a guard station at the Pentagon Heating and Refrigeration Plant.
Among the “first ever” applications demonstrated were:
• Solar air conditioning using solar heated air and a new desiccant-evaporative cooling cycle.
• Solar dehumidification of outside air using solar heated air for desiccant regeneration.
• High temperature solar air heating tile roofing with operating temperatures above 212 degrees Fahrenheit.
• Solar electricity generation and solar air heating from a single high temperature solar roof.
• Solar pre-heating and solar pre-cooling of an air source heat pump outdoor coil to reduce heat pump electricity use.
• Off-peak electricity for air conditioning and battery charging controlled by roof integrated daylight sensing solar electric panels.
The project was initiated by the Pentagon Energy Manger, Mr. Robert Billak (retired). Ms. Terry Watson was the project manager and technical lead (currently with the Smithsonian Institution) and Ms. Terri Robertson continued as project manager and technical lead upon her selection as
Pentagon Energy Manager. Ms. Tina Jenkins was the contracting officer.
Many others provided support and guidance toward the completion of this project. The staff of the Heating and Refrigeration Plant and Technical Division of Washington Headquarters Services and The Pentagon Force Protection Agency all provided support as the project progressed. EMO Energy, LLC performed many of the calculations necessary to refine the new solar air conditioning cycle from American Solar’s first guidance. Capital Sun Group installed the photovoltaics and battery power system.
It is our hope that the advances made with the sponsorship of the Pentagon will help educate others on the opportunities available to use simple solar heat recovery techniques from our building roofs and walls to provide savings in heating and cooling energy use.
We thank all the parties involved for their co-operation and support.
John Archibald
President, American Solar, Inc.
1
Introduction
The solar heating, air conditioning, power and lighting system installed at the guard station of the Pentagon Heating and Refrigeration Plant is one of the most advanced solar energy systems in the United States.
Despite its modest appearance, the system incorporates 12 advanced features that demonstrate new and improved ways of using solar energy to reduce fossil and electrical energy use.
It demonstrates these new and advanced technologies in a way that hides the advances within the conventional construction of a small 400 square foot building.
The guard station solar project incorporates the following 12 unique, advanced technologies:
1. Solar thermal tile air heating roof system 2. Reflective roofing
laminates and selective surface absorbers to boost solar roof air temperature 3. High temperature, multi-
stage solar roof with peak operating temperature above 212 degree F
4. Photovoltaics (PV) beneath solar thermal tiles for
electricity generation and heat production
5. PV panels separate from the solar roof for grid independent power generation and operation 6. Grid connected, off-peak, supplemental battery charging controlled by PV sensing relays 7. PV powered cooling fans for PV temperature control, switch gear cooling, and solar roof
heat recovery
8. Desiccant dehumidification of outside air using solar ‘waste heat’ in the summer 9. Solar heat driven desiccant-evaporative cooling of outside air
10. Solar pre-heating and pre-cooling of a heat pump to boost heat pump performance and cut electrical energy use
11. Rainwater recovery from the solar roof to supply the indirect evaporative cooling stages 12. Automatic winter tank drain-down to prevent freezing.
2 Many of these features have never before been demonstrated, such as the solar air heating tiles with PV absorbers below for electricity and heat production in one weather tight roof. The desiccant evaporative cooling system is also a unique development, since it relies on solar air heating to drive an air conditioning system using desiccant regeneration. The high temperature
solar hot air is an ideal energy source since desiccant regeneration is accomplished with hot summer airflow. In the wintertime, the solar roof supplies heating energy to the guard station.
The new, use of
photovoltaic materials in a heating system is made possible by the use of air as the heat transfer fluid under the solar thermal tiles.
Sunlight passing through the tiles hits the PV materials, which
simultaneously generate heat and electricity. The electricity runs the heating and cooling fans that collect solar heated air from the surfaces below the tiles. The electricity from the PV also energizes controls in the lighting and battery charging circuits.
Placing the PV system below the tiles keeps it warm, which improves the electric generating capacity of the amorphous PV panels. The fans also keep the PV cool enough (below 180 deg.
F) during peak summer conditions, to protect the panels from damage. The 68 watts of PV deployed below the roof surface represent just 3% of the total roof collector area. The PV panel surface area also contributes 345 watts of thermal air heating to the roof’s peak summer heating capacity of 11,700 Watts thermal (40,000 BTU/hr).
The new solar-desiccant-evaporative (SOLAR-DES-EVAP) air conditioning system is designed to reduce summer humidity levels of outside air and to cool the air before supplying it to the guard station. The desiccant drying stage removes the humidity from the air. The dry air allows ultra-efficient evaporative cooling to take place even in humid climates from the mid-Atlantic to the Gulf coast. This aspect of the system demonstrates how outside air can be pre-conditioning before entering an existing building HVAC system, using ‘excess’ solar heat in the summer.
This is particularly important for buildings like laboratories or industrial facilities with l00%
outside airflow and high energy use and cost in dehumidifying and cooling the air.
3 The SOLAR-DES-EVAP system has reduced dewpoint temperatures by as much as 16 degrees and reduced dry bulb temperatures by 10 deg F during a mid-day test in July. When minor adjustments are made to the water flow and airflow between stages, a 20+ degree drop in dry bulb temperature is expected. At peak performance, the existing system has demonstrated 3.6 units of cooling/dehumidification output for every unit of electrical input and all of the electrical input from the utility grid is at night, during ‘off-peak’ hours.
Other advanced features of the system are modern updates of several older solar heating technologies that were conceived during the 1970s and early 1980s, but never commercialized.
At that time, technologies such as solar assisted heat pumps were recognized as beneficial ways to cut energy use by heat pumps. Solar professionals understood that when solar heated air preheats the air entering a heat pump, the heat pump uses much less energy.
When the solar heat pump studies were done in the late 1970s, heat pump technology was at an early development stage and showed marginal efficiency improvement from solar pre-heating.
However, modern heat pumps, located at ground level and on the rooftops of many buildings, have overcome those inefficiencies and can substantially reduce energy use with solar pre- heating. During cold weather, heat pump energy use can be cut by 35% or more with the addition of solar air pre-heating systems. In many cases, there is ample flat roof space next to the roof top heat pumps to install simple solar air heating systems. Similarly, cooler air supplied to the heat pump in summer will cut electricity use by the heat pump in delivering air
conditioning. The Pentagon system was designed to demonstrate how solar air pre-heating and pre-cooling of heat pumps can cut high electricity use in the winter and summer.
The Pentagon system collects rainwater for the evaporative cooling stages because the guard station’s remote location has no ready source of water. Rainwater recovery was actually the lowest cost option, since installation of a ‘city’ water system would have required hand digging
Solar Thermal Tiles
Reflective Roofing
4 200 feet of trench over other utility lines buried under asphalt. However, the rainwater system offers other benefits, such as reduced storm water runoff from the roof, and reduced
consumption of ‘city’ water. This feature is even more important for arid, drought prone, locations, which can gain the greatest advantage from the evaporative cooling systems and which have the greatest need for water management. The PV system provides automatic pumping for the evaporative cooling stages and drain down for winter freeze protection.
The PV system is sized to supply all the power needed during the winter months. Power is delivered at 24 volts DC to a battery bank within the building. All fans and pumps are DC powered. The use of DC power instead of AC power saves energy in 3 ways. First it eliminates conversion losses from converting DC to AC power in an inverter. Second, the external rotor DC motors use about 1/3 of the power of comparable AC motors to moving the same amount of air. The third reason DC power saves energy is related to the use of peak demand reduction during summer cooling season.
During the peak air conditioning season in the summer, the SOLAR-DES-EVAP system will often consume more power than the PV panels can generate. The batteries provide the necessary capacity to operate the SOLAR-DES-EVAP system throughout the day. When the sun sets, the PV system activates a ‘110 Volt AC to 24 Volt DC’ battery charger that brings the batteries up to full charge during the nighttime hours. This hybrid battery charging approach makes the maximum use of the PV output during the peak electric demand and shifts the grid connected battery charging to an ‘off peak’ period when electrical demand on the utility grid is lower.
The project also provides several hundred square feet of usable covered storage space within the shed buildings.
Dumpster Pad
Guard station
E W True South
True North
110 VAC Panel board Air duct trunk
North Reflective Roof
Roof South Roof
PV panels
Heat Pump
0 4 8 12 16 20
Feet
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American Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE Aug 26 2004
Site Plan
AC-DC Battery Charger (floor) Storage Tank Draindown Solenoid (floor)
Storage Tank Draindown Manual Switch & Relay (wall) Head Tank Fill Pump & Run Dry Switch (floating in tank)
Storage Tank Draindown Thermostat (wall)
Head Tank Fill Pump Switch (rafter) Winter Heating Fan (wall)
Winter Heating Fan Switch (wall) Guard Station Supply Fan
Indirect Evap Cooler, IEVP2 fan Indirect Evap Cooler, IEVP1 fan
Heat Exchanger, HX1 fan Sump Drain Pump & Switch (inside bottom)
Head Tank & Float Switch (overhead) North Desiccant Supply Fan South Desiccant Supply Fan North Desiccant Regeneration Fan (wall) South Desiccant Regeneration Fan (wall) Desiccant Evaporative Cooling System
PV Shingles in Solar Tile Roof (4 in 2 lower courses)
PV Shingle Heat Recovery Supply Fans (2 below roof) PV Shingle Heat Recovery Exhaust Fan (below roof)
PV Shingle Heat Recovery Exhaust Fan (below roof) PV Shingle leads (2 pair below roof)
PV Shingle Leads (2 pair below roof)
Fan-Pump-Wheel Switches, See Switch Arr'g't dwg Interior Light
Exterior Light
Exterior light Interior light (rafter)
Solar Roof Temperature Snap Switch (roof deck)
110 Volt AC Panel Board Head Tank Fill Relay (rafter)
Rainwater Storage Tank Solar Roof Fan & Switch (rafter)
Batteries (floor)
Cooling SystemThermostat (1' above floor)
Heating System Thermostat (1' above floor) Interior Light Switch (beam)
Electrical Panels upper and lower
Air conditioning solenoid cooling fan
PV (+) disconnect switch
Building and system ground 110 VAC wall outlet Solar Charge Controller (beam)
Battery (+) disconnect switch South shed east wall
See details on elevation below
Photovoltaic Panels (2) 110 VAC wall outlet
Building & system ground
PV Shingle 9-13 Volt DC Disconnect Switch PV shingle 18-26 volt DC disconnect switch
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE
True South True North
W E
Equipment Location Plan View Aug 29 2004A
Plan View
North Elevation Electrical Controls
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American Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE Aug 26 2004
Guard Station
Sliding Gate
Air Duct
120 inin
Concrete Slab on Grade
180 inin Solar
Desiccant Evaporative
System Battery
Storage Water Storage
Pump & Piping Heat Pump
Air duct trunk
South Roof North Roof
Rainwater collection at gutters Head
tank
West Elevation
Reflective laminate over standing seam metal roof
solar tiles with PV below Elec.
Panels
AC-DC Battery Ch'rg'r solar tiles with
high temp absorber below
solar tiles with high temp absorber below Reflective Roof
Fence
Equipment Location West Elevation
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE Side Elevation Dimensions & Sun Angles 3/16"=1'-0"9 /24/03
324in
solar tiles PV below 22.5°
35.65°
solar tiles with black absorber surface below 122.82in
82.5in
reflective roof
180in 24in
86in
130in 22.5°
Concrete Slab on Grade
80in
solar tiles with high temp selective surface
30in
120in
35.7°
solar tiles with black absorber surface below 53.2°
Sun angle 21st of june
Example roof angles reflection lines
solar tiles with high temp selective surface
Assumes 400 sq ft at 16 ft long incl reflectors
78.76in 123.3in
100in
166in 49.25in
reflection line from opposite roof may,jun,jul for summer AC heat boost
99.34°
27.36°
22.91°
reflective roof
apr,aug
solar tiles PV below
nov jan aug
apr Sun angle 21st of june
Sun angle 21st of December
Valley shaded Nov, Dec, Jan
Generalized Roof and Sun Angle Diagram, approximate dimensions 37.02°
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE
PV Battery Load
Battery Solar Charge Controller
4 7 A
1 3
6 9 B
PV Shingles under solar tiles, 2 wired in series, 18-26 volt nominal, zero volts night Disconnect Disconnect
Disconnect
24 Volt DC AC-DC Battery Charger Batteries 24 Volt DC
18-26 volt daylight sensing bus
Daylight Sensing Relay Battery Charging Solenoid 24 Volt DC bus
PV shingle heat recovery fans and cooling fans for solenoids
9-13 Volt DC
Exterior Lights Air Conditioner Fans
Air Conditioner Pumps Water Tank Drain Down Solenoid Interior Lights
Heater Fan Relays and Contactors
To loads
PV panels 300 watt 24 Volt DC
110 Volt AC
None8/29/04
Electrical Schematic
Note See specific electrical circuits drawings for wiring connections
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE 1/32" = 1"Pentagon Solar Des. Evap Air Handler A
From Solar Roof
From Outside Air Exhaust to Outside To Guard Station
South Elevation, Solar Des. Evap Air Handler South Wall Panel Removed to show air flows
Outside Air Outside Air
Exhaust to outside air
IEVAP 1
evap media
drip pan
To solar roof
Outside Air
Sheet 1
IEVAP 1 recirc air
HX1 fan
HX1
Section at HX1 cross flow heat exchanger
showing air flow
Section at EVAP 1 heat exchanger showing air flow
Aug 29 2004
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE 1/32" = 1"Pentagon Solar Des. Evap Air Handler A
Sheet 2
South Elevation, Solar Des. Evap Air Handler South Wall Panel Removed to show component location
IEVAP 2, recirc fan
IEVAP 1 fan
Desiccant regen exhaust duct connection to solar roof /regen fan
transition evap media
HX1 cross flow plate heat xchngr IEVAP 1
IEVAP 2
desiccant cassette desiccant wheel
Desiccant Supply Air Fan water drip piping
Drain pan
recirc duct to North Side HX1 inlet
open screen, north side and below Sump Drain Pump
and Float Switch evap media Guard station]
supply fan
open screen, north and south sides
Aug 29 2004
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DWG NO REVAmerican Solar, Inc. 8703 Chippendale Court Annandale, Va. (703) 346-6053 www.americansolar.com
TITLE
2 2
2 3
4 5
Cooling Mode Schematic
Regeneration Air Evaporative Cooling Air Supply Air
897 CFM
188 CFM
187 CFM
4
5 3
Stage 1 Roof
Stage 2 Roof
188 CFM
1 897 CFM
Silica Gel Desiccant Wheel Type: WSG 440 x 200 3
IEVAP-1 PHE 500 28H-24S -.012
IEVAP-2 PHE 500 28H-24S -.012
188 CFM Outside Air
1 319 CFM
319 CFM 4 319 CFM
319 CFM
Outside Air 1 375 CFM
HX-1 PHE 500 28H -24S-.012 AHU
#1
#4
#3
#2
188 CFM
#5
#6
897 CFM 319 CFM
0
Evaporative Cooling Air
Supply Air
Stage T °F DB T °F WB Hum. Gr/# DA SCFM
0 95 76.1 105 187
1 86 89 375
2 150 33 375
3 112 33 375
4 81 33 375
5 63 33 188 IEVAP-2
Stage T °F DB T °F WB Hum. Gr/# DA SCFM
4 59.9 66 188
5 77.9 66 188
IEVAP-1
Stage T °F DB T °F WB Hum. Gr/# DA SCFM
1 95 76.1 105 897
2 77.9 134 897
3 90.2 134 897
Regeneration Air
Stage T °F DB T °F WB Hum. Gr/# DA SCFM
1 95 76.1 105 319
2 140 105 319
3 200 89 319
4 124 174 319
10/10/03
Solar Desiccant Evaporative Cooling Cycle Schematic
Regenerative Air Stream
CELdeck 5090 CELdeck 5090
Primary Supply Air Stream Secondary Air Stream
Performance During Design Conditions
Pentagon guard sta solar des evap 062904
06/29/04 09:56:2010:00:00 12:00:00 14:00:00 16:00:00 18:00:00 06/29/04 19:56:20
*F
60 80 100 120 140 160 180
Guard Sta supply 86.55
Grd sta supply Dew Pt 47.74
Solar roof (178.6)
Room floor temp (88.01)
06/29/04 14:10:39
www.americansolar.com Monitored performance test
of the Solar Desiccant Evaporative Cooling System Testing during an 80-90 degree F day showed inital installation of the indirect evaporative cooling system lowered delivered air temperature to the guard station by
about 7 degrees F. (Note: A later modification of the evaporative cooling system provided more stable cooling.)
Operation of the solar desiccant system lowered the delivered dew point temperature of the outside air by 10
degrees F, at solar temperature of 170-180 F.
www.americansolar.com
pentagon guard sta solar des evap71504
07/15/04 12:48:3113:00:00 14:00:00 15:00:00 16:00:00 07/15/04 16:48:31
*F
40 60 80 100 120 140
160 wb probe F
75.22 db probe F 83.67
grd sta sup T F (78.71)
Dew Point (*F) c:1 2 (64.96)
HX1 outlet T F 88.01
floor temp F 83.67 HX1 inlet T F 89.48
solar roof regen temp F 93.2
07/15/04 13:37:35
58 F supply dew point temp 91F Room Temp
80 F supply temp Indirect Evaporative cooling only, no
solar desiccant operation
Indirect evaporative cooling with solar desiccant operation
Monitored performance test
of the Solar Desiccant Evaporative Cooling System Testing during an 90+ degree F day showed the indirect evaporative cooling system lowered delivered air temperature to the guard station by as much as 17
degrees F.
Operation of the solar desiccant system lowered the delivered dew point temperature of the outside air by 6 degrees F, even though the solar temperature was at a low 130-150 F due to partly cloudy conditions.
Dry bulb and wet bulb probes were inserted downstream from IEVAP 1 @1:27PM, after HX1 @1:51, after desiccant wheel @2:04,
after HX1 @3:02 and after IEVAP 1@3:43PM. Temperature peaks in wet bulb curve are caused by drying of the wet bulb probe.
Pentagon guard sta3 5 04 S roof 2' cl
03/05/04 12:38:3912:40:00 13:00:00 13:20:00 13:40:00 14:00:00 03/05/04 14:18:39
Temperature (*F) c:2
60 80 100 120 140 160 180 200 220 240
*F
60 80 100 120 140 160 180 200 220 240
Air temp in absorber air flow channel (226.8)
PV outlet fan west exhaust temp (99.39)
PV upper course supply fan inlet air temp (78.01)
PV outlet fan east exhaust temp (108.43)
South building interior air temp 1' abv floor (73.15)
South wall metal panel temp (109.29)
air temp 1" below absorbers abv air duct outlet 180.48
03/05/04 13:51:09
www.americansolar.com Monitored Performance of the solar roof and solar
heating walls and roof integrated PV cooling system
During a 70 degree day, the heating performance of the solar components was monitored.
The PV cooling system maintained PV outlet air at less than 110 degrees F, and no more than 40 F
above ambient.
The solar heating walls reached operating temperatures of 115F, 40 F above ambient.
The roof stagnation temperature within the absorber air flow channel was generally 140F
above ambient.
The air stagnation temperature 1" below the absorber flow channel , at the air duct outlet, was
approximately 100 F above ambient.
Pentagon guard sta3/5-8/04 South roof 2' cl & PV fans
03/05/04 12:00:00 00:00:00 00:00:00 00:00:00 03/08/04 12:00:00
Temperature (*F) c:2
40 60 80 100 120 140 160 180 200 220 240 260
*F
40 60 80 100 120 140 160 180 200 220 240 260
Air temp in absorber air flow channel 242.6
PV outlet fan west exhaust temp (97.82)
PV upper course supply fan inlet temp (80.12)
PV outlet fan east exhaust temp (105.06)
03/07/04 12:49:09
www.americansolar.com Monitored performance of Roof integrated PV shingle
temperature cooling system.
The PV cooling fans force building air into the airspace above and below the PV shingles in the first two courses of
solar thermal tiles, to provide effective cooling of the PV shingles.
During an 80 degree day the PV shingle exhaust air temp was between 98 and 105 F while the unventilated roof
temperature stagnated at above 240 F. Maximum allowable operating temperature for the PV shingles is 190F, to protect the laminate. Monitored tests show that
the cooling fan and air flow design will maintain peak operating temperatures of the PV shingles well below the
maximum in all weather conditions.
Operating Instructions
The following Operating Instruction are provided to give both the theory of operations and the specific switch and controls alignments for successful operation of the systems.
The entire system is set to run automatically throughout the year without intervention by maintenance personnel.
Occasional observations of normal operations such as:
• air flow from the heat pump supply air duct,
• nighttime lighting,
• battery voltage levels read from the solar charge controller display,
• PV charging current read from the solar charge controller display,
• PV cooling fan operation as evidenced by indicator flag motion,
• Solenoid cooling fan operation as evidenced by airflow at the fan inlets
• rain gutter drainage during rainstorms,
• tank drain water flow to the pavement during the initial onset of cold weather and after any subsequent warm-cold cycles, and
• tank water levels,
will provide evidence of routine automatic operation.
5
Operating Instructions
Multiple voltage sources
There are 5 different power sources within the solar shed.
• The 300 Watt 24 Volt DC solar panels mounted outside the shed,
• The 68 watts of PV shingles installed within the solar roof supplying both 9-13 volt DC and 18-26 volt DC circuits,
• The 700 amp hour 24 volt DC battery bank,
• The 110 AC to 24 volt DC battery charger, and
• The 110 Volt AC convenience outlet powered from the nearby power panel Use caution when working on any circuit to ensure that all power sources are disconnected and exposed wires do not contact other circuits.
TO DISCONNECT POWER TO THE SYSTEM, turn OFF the following switches
• Turn OFF the PV Panel Disconnect Switch located on the horizontal beam below the electrical panels in the south building
• Turn OFF the AC-DC Battery Charger at the switch on the front cover of the charger. (For added protection, unplug the charger from the 110Volt AC outlet.)
• Turn OFF the Battery Disconnect switch located on the horizontal beam below the electrical panels in the south building. (The solar charge controller LCD display should go blank, indicating no power to the load circuits)
• Turn OFF the circuit breaker in the AC power panel located to the east of the solar shed buildings.
• Turn off the 9-13 Volt DC disconnect switch located on the exterior of the lower electrical panel west (tank) side.
• Turn off the 18-26 volt DC disconnect switch located on the exterior of the upper electrical panel east (door) side.
Note: Several wires are still energized within the building, up to the switches. These include:
• The PV panel leads,
• The PV shingle leads from the roof integrated PV shingles, and
• The Battery leads
USE CAUTION when working on any system and confirm a lack of voltage by proper use of test equipment.
Grounding
All DC circuits are negative ground.
The negative battery terminal is grounded.
The PV panels are grounded.
The metal building is grounded.
Two ground rods are placed near the fence and the air duct trunk.
The 110 Volt AC circuit is grounded at the AC power panel to the east of the building.
Use caution when working with any positive circuit to avoid contact with the metal building.
6
Operation of Systems
Interior Lights
All lights are 24 volt DC, 20 watt halogen lamps
A manual switch is located on the horizontal beam below the electric panels.
The one switch controls the interior lights in both parts of the shed.
Turn the light off when finished to preserve battery charge.
Exterior Lights
All lights are 24 volt DC, 20 watt halogen lamps.
The exterior lights are switched on and off automatically by a Daylight Sensing Relay in the bottom of the Upper electrical panel.
The relay is activated by power from two PV shingles installed in the southwest corner of the solar tile roof.
The shingles are wired in series to power the 18-26 volt bus.
The coil voltage is 18-26 volts nominal during daylight hours and will drop to 0 volts at night.
When the coil voltage drops to about 5 volts, the relay releases and the lighting circuit contacts are made.
The lights are powered from the 24 Volt DC bus which is energized by the batteries, and the solar charger, and the AC-DC charger.
To remove power from the exterior lighting circuit, turn the disconnect switch for the 18- 26 Volt DC bus to the OFF position. The switch is located on the exterior of the upper electrical panel on the east side. This removes power to the daylight sensing relay. It will also energize the AC-DC battery charger which is connected to the relay.
7
Batteries
There are (14) 12 volt, 100 amp hour sealed, advanced glass mat, deep cycle batteries.
The batteries are wired in series to create 700 amp hours capacity at 24 volts DC
Battery Charging
The batteries are charged by a combination of solar energy and 110Volt AC –24 volt DC battery charger.
The battery bank is charged by the 300 Watt separate solar panels during daylight hours and by the AC-DC battery charger at night.
The solar panels are constantly connected to the solar charge controller located on the beam near the electrical panels.
The solar charge controller will provide charging power whenever there is sufficient sunlight to energize the solar panels.
The solar charge controller operates on a monthly charging cycle with varying voltage to the batteries to maintain peak performance.
The AC-DC battery charger is constantly turned on.
The AC-DC battery charger is constantly connected to the battery negative lead.
The positive lead of the AC-DC charger is connected via a disconnect switch, to a DC solenoid (contactor) located in the lower electrical panel.
The contactor is energized by the daylight sensing relay (relay is also used for exterior lighting control)
During daylight hours, the solenoid contacts are open and the AC-DC battery charger positive lead is disconnected from the batteries.
During night time, the daylight sensing relay releases and the relay contact to the solenoid is broken, releasing the solenoid, which closes the contact for the AC-DC battery charger positive lead to the batteries.
The AC-DC battery charger will provide the finishing charging of the batteries that the solar panels may not have provided during the day.
Caution: The Solar panels may still provide a positive charge even when the AC- DC battery charger is operating. However, in most cases, the AC-DC charger will operate at higher voltage than the solar panels when operating at dawn and dusk.
Always assume the solar panels are providing a positive charge to the batteries unless the solar panels are disconnected from the charge controller.
Caution: The battery charging solenoid (contactor) consumes about 2.4 watts of power when energized during the daytime.
Heat buildup in the solenoid is dissipated by the cooling fan.
Cooling airflow is from outside the panel, across the solenoid, and out the edges of the front cover of the panel.
DO NOT close the front covers of the electrical panels tightly or cooling air flow will be greatly reduced and the solenoid will fail prematurely.
8
Solar PV Shingles in Solar Roof
There are (4) 17 watt PV shingles in the south solar roof.
The PV shingles are located under the first two courses of solar tiles in the south roof, two per course.
The active area of the shingle is approximately 5 inches high and 86 inches long.
The PV shingles generate 9 volts at max power and 13 volts open circuit.
The electric leads from the PV shingles penetrate through the metal roof deck in ½”
metal conduit.
The PV shingles provide both solar heat and electric power for controls and cooling.
The temperature of the PV shingles must not exceed 200 degrees F or the encapsulating laminate will degrade.
The solar roof has been configured with supply and exhaust fans arranged to ventilate the PV shingle to ensure the temperatures do not reach 200 F.
Supply fans are in the middle of the roof.
Exhaust fans are at the ends of the roof.
The fans are directly connected to the PV shingle leads and operate at a nominal 12 volt DC (9-13 VDC).
Two fans in the electrical panels are powered by one of the PV shingles on the door (east) side of the shed.
The fans in the electrical panels provide cooling air for the solenoids (contactors) in the panels.
To disconnect the power to the fans in the electrical panel, turn the 9-13 volt DC
disconnect switch to the OFF position. The switch is located on the outside of the lower electrical panel on the west side.
To disconnect the power to the supply and exhaust fans that are installed below the PV shingles, remove the wire nuts at the PV shingle leads.
Use caution to protect the disconnected wire from inadvertent contact with other circuits or metal building components.
9
Solar Heat
The north solar roof is used to provide heat in the winter to the guard station heat pump.
Solar heated air is drawn from the solar tile roof system and sent to the outdoor coil of the heat pump.
The heat is controlled by a thermostat located about 1’ above the floor, near the door below the electrical panel.
Note: There are two thermostats below the electrical panels. The heating thermostat is nearest the door. The cooling thermostat is nearest the center of the building.
The thermostat energizes a relay located in the lower electrical panel.
The relay powers the solar heating fan.
The thermostat and relay coil circuit are energized from the 24VDC bus.
The heating fan is energized from the 24 Volt DC bus and is protected by an in-line fuse located in the lower electrical panel.
When the thermostat senses temperature in the building below the set point (~50F) the thermostat closes a relay to energize the heating fan.
The fan will run even during nighttime hours as long as the temperature is below the thermostat set point.
Through the evening, this will extract all the heat built up within the roof during the day, and will begin the extraction earlier in the morning than would occur with more
complicated ‘on–off’ roof temperature controls.
However, the 120 watt fan may run for several hours during cold nights when the roof has reached ambient temperatures and no useful heating is provided. This causes no harm to the system.
During sunny daytime hours, the heater will provide air to the heat pump that is about 40 degrees above ambient temperatures.
To turn the fan off, there is a local toggle switch on the south wall of the north shed, near the duct and cable trunk.
The toggle switch should be left on for automatic operation using the thermostat and relay.
Caution: Do not set the heating thermostat above the minimum setting as it will cause the heater fan to run during warm days when no heating is required.
Excessively high temperature across the heat pump outdoor coil during the heating season can be detrimental to the heat pump.
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Solar air conditioning
The solar air conditioning system uses
• solar heated air from the solar roof
• a desiccant wheel
• plate heat exchangers, and
• evaporative cooling using collected rainwater,
to provide cool dry air across the guard station heat pump outdoor coil.
This solar desiccant evaporative (SOLAR-DES-EVAP) cooling system uses solar heated air to reduce humidity and lower temperature with less electricity use than conventional air conditioning systems.
Power
The solar air conditioning system is powered by the 24 volt bus.
Most fans and pumps and the desiccant wheel are separate circuits with separate local toggle switches near the device and a separate fuse located in the 2 fuse blocks on the rear wall of the upper electrical panel. The exception is the three small fans for the Indirect Evaporative Cooler #1 (IEVP1), Heat Exchanger #1 (HX!) and the Guard Station Supply Fan. These three fans are on a single circuit fed by one fuse in the lower fuse block. Each fan has a local toggle switch on the south east corner of the SOLAR-DES-EVAP system.
Both fuse blocks are connected to a single solenoid (contactor) located on the lower right side of the upper electrical panel.
When the solenoid is energized, the entire air conditioning system is activated.
Caution: The air conditioning solenoid (contactor) consumes about 2.4 watts of power when energized during the summer daytime hours.
Heat buildup in the solenoid is dissipated by the cooling fan.
Cooling airflow is from outside the panel, across the solenoid, and out the edges of the front cover of the panel.
DO NOT close the front covers of the electrical panels tightly or cooling air flow will be greatly reduced and the solenoid will fail prematurely.
The total load on the system with all circuits energized is 750 watts.
ON-OFF Control
The system operates in response to a cooling thermostat located 1’ above the floor below the electrical panels toward the center of the south shed.
Note: There are two thermostats below the electrical panels. The heating thermostat is nearest the door. The cooling thermostat is nearest the center of the building.
The thermostat set point is 88 degrees F.
The thermostat circuit also contains a snap switch below the center of the solar roof in the south shed and a relay located on the upper right side of the upper electrical panel to power the solenoid.
The roof snap switch closes at 110F and above and opens at 90F and below.
The thermostat, snap switch, and relay coil circuit is energized from the 24VDC bus.
The fans and pumps are energized at the fuse block terminals from the Solar Charge Controller (+) & (-) “LOAD” connections, which are at 24 Volt DC.
11 The fuse block (-) terminals are wired directly to the (-) LOAD terminal. The Fuse block (+) terminals are connected via the Air Conditioning Solenoid (contactor) to the (+) LOAD terminal.
When the thermostat senses a room temperature above 88 degrees and a roof
temperature of at least 110 degrees, the thermostat circuit is closed and the relay coil is energized.
The relay contacts complete the circuit to the Air Conditioning Solenoid (contactor) to close the solenoid and connect the (+) wire to the fuse blocks, energizing all the air conditioning components.
The entire air conditioning system can be turned off by turning the thermostat ‘Off-Cool’
switch to OFF.
This opens the thermostat circuit and prevents the relay coil from energizing the solenoid.
Note: The ‘Fan-Auto’ switch on the thermostat is disconnected and inactive.
All fan and pump switches in the air conditioning system should be left ON, with the exception of the Sump Drain Pump Manual Switch which should be left OFF.
Water System
The Sump Drain Pump Manual Switch is provided to reduce the water level in the sump. It will only operate when the air conditioning solenoid is energized.
It will not pump the sump dry.
Caution: DO NOT run the Sump Drain Pump continuously using the Manual Switch when the sump is dry or at the lowest pumping level, as the pump can be damaged.
Monitor pump flow at the return to the storage tank to determine an appropriate manual shut off time.
When the air conditioning system is running, water is pumped from the storage tank to the head tank until the head tank float switch indicates full and closes the internal switch in the float.
The switch energizes a relay coil located in an electrical box in the rafter below the reflective roof of the south shed. The relay opens the contact for the head tank fill pump to shut the pump off.
The water in the head tank flows by gravity into the evaporative coolers and to the sump.
When the sump is full, a float switch in the sump energizes the Sump Drain Pump to pump water back to the storage tank.
Air System
Room air is blown in to the Solar Desiccant Evaporative (SOLAR DES EVAP) Cooling System from two blowers at the front of the unit near the door.
This supply air passes through the bottom half of a rotating desiccant wheel which removes the humidity from the air but heats the air in the process.
Simultaneously, solar heated air from the solar roof is drawn through the upper half of the rotating desiccant wheel to continuously regenerate the desiccant and carry away the moisture taken out of the supply air.
The warm moist air is exhausted out the north side of the shed by two blowers located on the north wall.
12 The warm dry supply air within the Solar Des Evap passes through a plate heat
exchanger (HX1) which uses room air on one side of the plate to cool the supply air.
The hot exhaust air from this process is carried to the south building where it is used to raise the entering air temperature of the first stage of the solar roof.
A small fan mounted on the north wall/roof of the south shed draws solar heated air from the south roof to raise the entering air temperature of the north solar roof.
The north solar roof air is used for the desiccant regeneration.
The supply air within the SOLAR DES EVAP continues to move through the first
indirect evaporative cooler (IEVP1) composed of another plate heat exchanger which is above an evaporative cooling pad.
Water is sprayed into the heat exchanger and falls down over the pad.
Room air flows up through the pad and heat exchanger and is cooled to near the wet bulb temperature by the evaporating water.
The exhaust of this moist air is sent out the North wall of the North shed.
The supply air is separated from the moist air so it remains dry and is cooled slightly.
The supply air is then divided into two air streams.
One air stream continues through the next evaporative cooler (IEVP2) to the guard station supply fan and on to the heat pump outdoor coil.
The other air stream is used to drive the evaporative cooling process to cool the first air stream.
The evaporative stream descends below and then up through an evaporative pad and a plate heat exchanger and is exhausted back to the air intake for the first heat
exchanger, HX1.
This cool dry air moving though IEVAP2 provides deeper cooling of the supply air stream headed toward the guard station and the exhaust of the moist air from IEVAP2 is cooler than the room air, so it adds to the cooling of HX1.
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Storage Tank, Drain Down and Run Dry
The Storage Tank collects rainwater from the three roof gutters.
It is sized to collect and store enough water during a month to operate the evaporative coolers for one month, using typical monthly rainfall.
During uncommonly dry months, the tank may be pumped down to a low level in the course of supplying water for the SOLAR DES EVAP system.
The Head Tank Fill Pump, floating with in the storage tank, is not designed to run dry continuously. To prevent damage to the pump at low tank water levels, a float switch has been attached to the pump platform, which will shut the pump off when the water level falls below the pump minimum pumping level.
To prevent freezing damage to the tank, the tank is designed to be drained dry when temperatures go below 40 F.
The tank has been sloped to the drain on the south west corner and is supported on a combination of wood blocks and foam pads at several points.
The drain down circuit uses a solenoid operated valve in a low point drain line on the floor at the west wall of the south shed.
The valve is normally closed and the solenoid is not energized.
When a thermostat senses the temperature is below 40F, the thermostat closes and energizes a relay installed in an electrical box on the west wall above the solenoid valve.
The thermostat is located on the North Wall of the south shed near the piping.
The relay energizes the solenoid valve which opens and drains the tank.
A manual switch is available on the cover of the relay electrical box to manually drain the tank.
Note: Be sure the solenoid switch is turned off when not manually draining the tank.
The thermostat and relay and solenoid valve are energized by the 24 Volt DC bus.
The circuit is constantly energized and has an inline fuse on the bottom of the upper electrical panel.
