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.
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, multistage 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.
1
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.
2
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.
Solar Thermal Tiles
Reflective Roofing
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 preheating. 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
3
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.
4
Dumpster
Pad
Reflective
Roof
W
True
North
True
South
E
20
Guard
station
Heat Pump
North
Roof
South
Roof
PV panels
110 VAC
Panel board
Aug 26 2004
Air duct trunk
DATE
16
SCALE
12
DWG NO
8
Site Plan
4
TITLE
0
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
Feet
SHEET
REV
Indirect Evap Cooler, IEVP2 fan
Winter Heating Fan (wall)
Winter Heating Fan Switch (wall)
Storage Tank Draindown Thermostat (wall)
Rainwater Storage Tank
Solar Roof Fan & Switch (rafter)
Head Tank Fill Relay (rafter)
Exterior light
110 Volt AC Panel Board
Interior light (rafter)
110 VAC wall outlet
Building & system ground
Head Tank Fill Pump Switch (rafter)
Head Tank Fill Pump & Run Dry Switch (floating in tank)
Storage Tank Draindown Manual Switch & Relay (wall)
See details on elevation below
Storage Tank Draindown Solenoid (floor)
Solar Roof Temperature Snap Switch (roof deck)
PV Shingles in Solar Tile Roof (4 in 2 lower courses)
Photovoltaic Panels (2)
Batteries (floor)
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 Heat Recovery Supply Fans (2 below roof)
PV shingle 18-26 volt DC disconnect switch
South shed east wall
Electrical Panels upper and lower
Air conditioning solenoid cooling fan
PV Shingle 9-13 Volt DC Disconnect Switch
Interior Light Switch (beam)
Solar Charge Controller (beam)
Battery (+) disconnect switch
Cooling SystemThermostat (1' above floor)
110 VAC wall outlet
Building and system ground
Heating System Thermostat (1' above floor)
North Elevation Electrical Controls
Aug 29 2004
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
AC-DC Battery Charger (floor)
PV Shingle leads (2 pair below roof)
PV (+) disconnect switch
DATE
Guard Station Supply Fan
Sump Drain Pump & Switch (inside bottom)
SCALE
South Desiccant Regeneration Fan (wall)
Exterior Light
Head Tank & Float Switch (overhead)
North Desiccant Supply Fan
South Desiccant Supply Fan
Fan-Pump-Wheel Switches, See Switch Arr'g't dwg
Interior Light
Heat Exchanger, HX1 fan
SHEET
A
REV
True South
North Desiccant Regeneration Fan (wall)
Indirect Evap Cooler, IEVP1 fan
DWG NO
Desiccant Evaporative Cooling System
Equipment Location Plan View
E
W
TITLE
True North
Plan View
Guard Station
Air Duct
Air duct trunk
Solar
Desiccant
Evaporative
System
solar tiles with
high temp
absorber below
South Roof
solar tiles with
high temp
absorber below
Elec.
Panels
solar tiles
with PV below
Water Storage
Pump & Piping
120 inin
AC-DC
Battery
Ch'rg'r
180 inin
Concrete Slab on Grade
Battery
Storage
Rainwater collection
at gutters
DATE
Aug 26 2004
SHEET
REV
SCALE
Head
tank
Reflective laminate
over standing seam
metal roof
DWG NO
Reflective Roof
North Roof
Equipment Location West Elevation
Sliding Gate
TITLE
Heat Pump
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
West Elevation
Fence
123.3in
22.91°
27.36°
apr,aug
78.76in
35.7°
solar tiles with
black absorber surface below
reflective roof
37.02°
solar tiles PV below
Valley shaded Nov, Dec, Jan
100in
Assumes 400 sq ft at 16 ft long incl reflectors
166in
TITLE
Generalized Roof and Sun Angle Diagram, approximate dimensions
solar tiles
with high temp
selective surface
86in 80in
122.82in
82.5in
130in
reflective roof
22.5°
35.65°
22.5°
solar tiles PV below
30in
120in
180in
24in
Concrete Slab on Grade
324in
solar tiles with
black absorber surface below
9 /24/03
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
49.25in
53.2°
DATE
99.34°
solar tiles
with high temp
selective surface
3/16"=1'-0"
Sun angle
21st of December
reflection line from opposite roof
may,jun,jul for summer AC heat boost
SCALE
Example roof angles reflection lines
SHEET
REV
nov
jan
DWG NO
aug
apr
Side Elevation Dimensions & Sun Angles
Sun angle
21st of june
Sun angle
21st of june
SHEET
REV
PV panels 300 watt 24 Volt DC
To loads
24 Volt DC bus
Air Conditioner Fans
Air Conditioner Pumps
24 Volt DC
Water Tank Drain Down Solenoid
AC-DC Battery Charger
110 Volt AC
Heater Fan
Relays and Contactors
1
18-26 volt daylight sensing bus
3
4
6
7
9
A
B
Exterior Lights
Disconnect
Daylight Sensing Relay
PV Shingles under solar tiles, 2 wired in series, 18-26 volt nominal, zero volts night
Battery Charging Solenoid
PV shingle heat recovery fans and
cooling fans for solenoids
9-13 Volt DC
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
Disconnect
TITLE
Batteries 24 Volt DC
Interior Lights
DATE
Disconnect
None
Load
SCALE
Battery
DWG NO
PV
Electrical Schematic
Battery Solar Charge Controller
8/29/04
Note See specific electrical circuits drawings for wiring connections
South Elevation, Solar Des. Evap Air Handler
South Wall Panel Removed to show air flows
Exhaust to
outside air
To solar roof
HX1 fan
IEVAP 1
recirc air
Outside Air
IEVAP 1
evap media
Outside Air
HX1
Outside Air
drip pan
Section at HX1 cross flow
heat exchanger
showing air flow
Section at EVAP 1 heat exchanger
showing air flow
1/32" = 1"
DATE
Aug 29 2004
SHEET
A
REV
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
TITLE
From Outside Air
SCALE
To Guard Station
DWG NO
Exhaust
to Outside
Pentagon Solar Des. Evap Air Handler
Sheet 1
From Solar Roof
water drip piping
IEVAP 1
Desiccant Supply Air Fan
desiccant wheel
transition
evap media
Sump Drain Pump
and Float Switch
Drain pan
desiccant cassette
evap media
open screen,
north and
south sides
HX1 cross flow plate heat xchngr
open screen,
north side and below
South Elevation, Solar Des. Evap Air Handler
South Wall Panel Removed to show component location
TITLE
IEVAP 2
DATE
Aug 29 2004
SHEET
A
REV
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
Guard station]
supply fan
1/32" = 1"
Desiccant regen exhaust
duct connection to solar
roof /regen fan
SCALE
recirc duct to North Side HX1 inlet
DWG NO
IEVAP 1 fan
Pentagon Solar Des. Evap Air Handler
Sheet 2
IEVAP 2, recirc fan
188 CFM
#5
188 CFM
0
Outside Air
187 CFM
#1
2
AHU
Silica Gel
Desiccant Wheel
Type: WSG 440 x 200
1 375 CFM
2
HX-1 PHE
500 28H
-24S-.012
3
3
3
IEVAP-1
PHE 500
28H-24S
-.012
319 CFM
5
4
IEVAP-2
PHE 500
28H-24S
-.012
Regenerative Air Stream 319 CFM
#6
4
2
CELdeck 5090
188 CFM
5
CELdeck 5090
Primary Supply
Air Stream
4
#2
188 CFM
Outside Air
1
1
319 CFM
#3
319 CFM
897 CFM
897 CFM
Evaporative Cooling Air
#4
Performance During Design Conditions
Supply Air
Stage T °F DB
0
95
1
86
2
150
3
112
4
81
5
63
T °F WB
76.1
Hum. Gr/# DA
105
89
33
33
33
33
SCFM
187
375
375
375
375
188
IEVAP-1
Stage T °F DB T °F WB
1
95
76.1
2
77.9
3
90.2
Hum. Gr/# DA
105
134
134
SCFM
897
897
897
IEVAP-2
Stage T °F DB T °F WB
4
59.9
5
77.9
Hum. Gr/# DA
66
66
SCFM
188
188
Regeneration Air
Stage T °F DB T °F WB
1
95
76.1
2
140
3
200
4
124
Hum. Gr/# DA
105
105
89
174
SCFM
319
319
319
319
10/10/03
DATE
897 CFM
Secondary
Air Stream
SCALE
Supply Air
SHEET
REV
Evaporative Cooling Air
Stage 2 Roof
DWG NO
Regeneration Air
Solar Desiccant Evaporative Cooling Cycle Schematic
Cooling Mode Schematic
TITLE
319 CFM
American Solar, Inc.
8703 Chippendale Court Annandale, Va.
(703) 346-6053 www.americansolar.com
Stage 1 Roof
Pentagon guard sta solar des evap 062904
Guard Sta supply
86.55
Grd sta supply Dew Pt
47.74
Solar roof
(178.6)
Room floor temp
(88.01)
180
06/29/04 14:10:39
160
140
Monitored performance test
of the Solar Desiccant Evaporative Cooling System
*F
120
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.
100
80
60
www.americansolar.com
10:00:00
06/29/04 09:56:20
12:00:00
14:00:00
16:00:00
18:00:00
06/29/04 19:56:20
pentagon guard sta solar des evap71504
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
140
Indirect evaporative cooling with solar
desiccant operation
120
07/15/04 13:37:35
Indirect Evaporative cooling only, no
solar desiccant operation
100
*F
91F Room Temp
80
80 F supply temp
www.americansolar.com
60
58 F supply dew
point temp
40
13:00:00
07/15/04 12:48:31
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.
14:00:00
15:00:00
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.
16:00:00
07/15/04 16:48:31
Pentagon guard sta3 5 04 S roof 2' cl
240
240
220
220
200
200
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
180
160
Monitored Performance of the solar roof and solar
heating walls and roof integrated PV cooling
system
160
*F
Temperature (*F) c:2
180
During a 70 degree day, the heating performance
of the solar components was monitored.
140
140
120
120
100
100
80
80
60
60
12:40:00
03/05/04 12:38:39
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.
13:00:00
13:20:00
13:40:00
14:00:00
03/05/04 14:18:39
www.americansolar.com
260
Pentagon guard sta3/5-8/04 South roof 2' cl & PV fans
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)
240
240
220
220
200
200
Monitored performance of Roof integrated PV shingle
temperature cooling system.
180
180
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.
160
160
03/07/04 12:49:09
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.
*F
Temperature (*F) c:2
260
140
140
120
120
100
100
80
80
60
60
www.americansolar.com
40
40
03/05/04 12:00:00
00:00:00
00:00:00
00:00:00
03/08/04 12:00:00
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.
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.
5
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 1826 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.
6
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 ACDC 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.
7
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.
8
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.
9
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.
10
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.
11
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.
12
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.
13