**Night Sky Radiant Cooling System Saves Energy**

**in a Commercial Building**

This night-sky radiant cooling system enables downsizing of conventional
cooling equipment and reduces annual energy costs by cooling water in a
radiative and evaporative fashion. Water is sprayed over a flat or
low-slope roof surface at night, filtered, stored, and delivered the
following day for cooling. The system is comprised of a roof-spray
assembly, a thermal-storage component, and a microprocessor control
unit. The process is most applicable to arid climates where hot days are
followed by cool nights with minimum temperatures below 18°C. The
product was tested in ![](media/image1.png){width="2.8534722222222224in"
height="1.6881944444444446in"}a Los Angeles, California state government
office building. Operationally, system storage water is sprayed over the
low-slope single-ply membrane roof, which is divided by a north-south
ridge. The spray water, typically chilled to 5-10°C below the minimum
night air temperature, from the east and west roof sections is collected
at roof drains, filtered, and delivered to separate thermal storage
locations. Water from the east roof section is stored in an underground
tank north of the building. This tank water is delivered on thermostat
demand to custom cooling coils added at rooftop HVAC units, serving a
large open plan section of the building. The water chilled on the west
roof slope is also filtered, and then circulated through underfloor
plastic tubing to store cooling in the concrete slab floors of rooms
located along the west and south walls. This passive radiant cooling
from the floors provides first-stage cooling for these areas, with
second-stage cooling provided by twelve small rooftop HVAC units. Annual
cooling-energy consumption was reduced by more than 50%.

**Technical Data**

The system installed includes a copper and brass roof-spray assembly
composed of piping, pumps, sand filters, and spray heads, an underground
fibreglass storage tank (56.9 m^3^), plastic under-floor tubing (approx.
2,700 m), and four chilled-water coils. Typical capacities are 3.4 MJ/m2
of roof surface in peak conditions. For buildings with peak loads
exceeding this amount, WhiteCap™ allows for significant downsizing of
conventional cooling equipment.

**Energy Data**

Conventional cooling-energy consumption was over 70% lower with
WhiteCap™ operation in September than without WhiteCap™ in July.
Adjusting for WhiteCap™ pump energy use and climate changes, net annual
cooling-energy savings are over 50% (over 74.4 GJ saved annually).

**Economic Data**

Simple payback period is less than 2.5 years. The cost of the WhiteCap™
system totalled USD 10,100, with annual savings of USD 4,400.

**Contacts:**

+------------------------------------+---------------------------------+
| 5401 Associates, L.P.              | Roof Science Corporation        |
|                                    |                                 |
| K Brunk                            | M. Best                         |
|                                    |                                 |
| 2901 Ocean Park Boulevard, Suite   | 123 C Street                    |
| 117                                |                                 |
|                                    | Davis, CA 95616                 |
| Santa Monica, CA                   |                                 |
|                                    | 916-753-4844                    |
| 310-396-4161                       |                                 |
|                                    | 916-753-4125 (Fax)              |
| 310-396-8910 (Fax)                 |                                 |
+------------------------------------+---------------------------------+
| Davis Energy Group                 |                                 |
|                                    |                                 |
| D. Springer                        |                                 |
|                                    |                                 |
| 123 C Street                       |                                 |
|                                    |                                 |
| Davis, CA 95616                    |                                 |
|                                    |                                 |
| 916-753-1100                       |                                 |
|                                    |                                 |
| 916-753-4125 (Fax)                 |                                 |
+------------------------------------+---------------------------------+

***See also: "Nightsky" System Cools Roof Tops***

***NightSky natural cooling system saves energy***

***WhiteCap™ Roof Spray Cooling***