Novel Evaporative Technologies

•The recent advent of "Dew Point" cooling provides a new and highly economical commercial evaporative cooling technology.

•Taking design cues from the acient Roman hypocaust, the Integrated Evaporative technique demonstrates a genuine potential for widespread applicability.

Direct Evaporative

Suitable only for dry climates where additional moisture is desirable

Dew Point Evaporative

Can approach dew point temps, but works best in dry climates

Dew Point cooling systems are, by far, the most efficient commercially available cooling systems to date. They consume ten to twenty percent of the power consumed by a typical vapor compression system. Widespread utilization of "Dew Point" technology will not only lower the cost of human comfort, the technology will prove beneficial in many other aspects. Foremost is lower peak power demand. Overly high peak power demand strains the utility grid to its limit. Also, less overall power produced means lower greenhouse gas emissions and fewer environmental issues. Additionally, water conservation is aided by reduced power production. Water is used as a coolant by most power generating facilities. Lower power production has an associated lessening of water use. Water conservation is an issue that is not often tied to power reduction; however, it is a factor that will be increasingly critical in the coming years. An attendant reduction in dependence on fossil fuels will also have political benefits.

An evaporative air conditioner capable of approaching dew point temperatures has the potential to provide comfort even in the humid southeastern United States – in the daytime. During the day, there is sufficient dew point depression (the difference between ambient dry bulb temperature and the concurrent dew point temperature) to yield cooling comfort. After the sun goes down however, the dry bulb temperature and the dew point temperature come much closer together. This loss of dew point depression at night substantially reduces the cooling potential of commercial dew point cooling systems. At night, they cannot provide cooling in the human comfort range.

IE systems are subject to the same climatological limitations as a commercial dew point cooler. However, the IE system has a physical advantage that allows it to provide cooling comfort at night – high thermal mass. The high thermal mass of the perimeter walls and floor serve as a giant heat sink. The floor and walls provide a "cave effect" and continue to deliver cooling comfort at night. Formally referred to as thermal inertia, the "thermal flywheel effect" of the IE system makes it the only air conditioning system capable of "coasting" over night. This feature not only broadens the applicability of the system, it also improves economic performance. Powering the system 12 hours a day rather than 24 hours a day doubles economic efficiency. None of these advantages can be duplicated by centralized systems.

In the summer of 2005 a subscale prototype of the Integrated Evaporative system was constructed and demonstrated in Panama City, Florida.

Prototype features:

• Lava rock filled floor and walls

• A living space area of 80 cubic feet and 28 cubic feet of lava rock

• Air was transported through the walls and floor via a 100w centrifugal blower

• Drip rails supplied water at the top of lava bed within the walls

• The interior walls were tightly joined so no air could short-circuit the designed path
• No attempt was made to control interior humidity

An air inlet was fashioned in the base of the prototype floor. The floor and walls were filled with absorbent, lava rock gravel. A centrifugal exhaust fan above the ceiling provided air flow through the floor and walls. A drip rail above each wall served as a water supply. A temperature data logger was suspended in the living space center.

The graph at right indicates ambient and prototype interior temperatures, as well as ambient relative humidity. Noted at top are the midday peak temperature differentials.

The chart at right is a listing of temperatures that can be delivered by "swamp coolers".

Indicated in bright green is the performance (83°F) of the prototype at mid-day on July 24, 2005 with an ambient temp of 102°F and RH of 49%. Indicated in dark green is the typical performance (90°F) of a swamp cooler at given ambient conditions.

Placing the evaporator within the perimeter walls and floor yields IE's greatest advantages over centralized systems: "Dynamic Insulation" and "Thermal Flywheel" effect

• Outdoor heat and indoor heat are both absorbed by evaporating water within the gravel bed.

• Heat that migrates to the evaporator is vented outside the building.

• Decentralized evaporator yeilds a 100% effective thermal barrier within the floor and walls when the system is running.

• High mass and high specific heat capacity of liquid water, concrete, and rock gravel yield a very large thermal mass.

• High thermal mass provides a pronounced "thermal flywheel effect".

• Thermal flywheel continues to provide human comfort when the system is idle.

Indirect Evaporative

Works best in dry climates

Integrated Evaporative

Provides temperatures within the human comfort range in humid climates