Commercial AC The ROI on Energy Saving HVAC Alternatives

Return on Investment for Green Heating and Cooling Systems

According to the US Department of Energy, heating and cooling account for 56 percent of a home’s total energy use.  With rising fuel costs and the depletion of natural resources, energy conservation has become a focal point of research in recent years.  Some of the most commercially viable next-gen green HVAC technologies are geothermal heating and cooling, chilled beam systems, night-sky cooling, and thermal energy storage.  So how do these systems compare, and what kind of return on investment (ROI) can homeowners and business owners expect from them?

Geothermal

Geothermal heating and cooling rely upon the earth’s tendency to maintain a moderate temperature just below the surface.  A few feet below the surface, water temperature remains constant throughout the year, somewhere between 40 and 80 degrees Fahrenheit, depending on location.  Geothermal air conditioning and heating systems use the earth below the surface as a heat sink, or heat source, depending on the time of year, to improve the efficiency of HVAC systems.

ROI for Geothermal Systems

There are several factors to take into account when weighing the costs and benefits of a geothermal HVAC system, including tonnage, method of pipe installation, and whether the home is a suitable site for geothermal HVAC installation.  Homeowners can typically expect about a 20-30% reduction in monthly energy bills from a geothermal system, in addition to federal tax credits covering up to 30% of the cost of the entire system.  On the cost side of the equation, geothermal systems will cost about $1000 more per ton of capacity, and installation may cost up to $10,000-20,000.  As a general rule of thumb, a geothermal HVAC system should pay for itself in about ten years, and continue giving benefits for as long as you own your home.  Geothermal systems also typically last twice as long as electrical heating and cooling systems.

Chilled Beam System

Chilled beam cooling systems are used extensively in Europe, and are just starting to become common in the US.  Chilled beam air conditioning systems circulate cool water through a network of tubes in the ceiling, and sometimes in the floor.  When the cool water hits the warm air in a room, the cool air sinks into the room, due to cool air having a higher density than warm air.  Based on this simple principle, the cool air diffuses throughout the room.  Water is also a more efficient carrier of energy than air, thus resulting in efficiency gains.  Another advantage of chilled beam cooling systems is that they eliminate the need for heating and cooling ducts and fans.  They also typically do not recycle air like conventional air conditioners, so fresh air can be brought in throughout the day.

ROI for Chilled Beam Systems

Although chilled beam systems are slightly more expensive due to the novelty factor, they are 25-30% more energy efficient, and are therefore highly recommended, particularly for newer and larger buildings.  For example the Genomic Science Building at the University of North Carolina was recently able to lower its HVAC costs by 20% by using chilled beam technology.

Night-Sky Cooling

We’ve all experienced how useful it can be to open the windows after a hot day to bring in cool air.  Night-sky cooling systems expand on this principle of harnessing the coolness of the night air by spraying water over the roof at night, which then cools and is collected in a thermal storage tank.  The stored cool water is then spread through tubes in the floor or ceiling during the day to cool the air.  So naturally, night-sky cooling works well in tandem with a chilled beam system as an advanced cooling system to create energy efficient homes and buildings.

ROI for Night-Sky Cooling

Night-sky cooling will be most effective in climates such as deserts, which get extremely hot during the day and cold at night.  A recent report from the state government of New Mexico estimated that an 1800 square foot home using diffusive night-sky cooling could cut energy use in half, and recoup the cost of the system in just a few short years.

Thermal Energy Storage

Thermal Energy Storage (TES) systems work by using the most electricity when it is least expensive, at off-peak hours. This results in less strain on electrical grids during peak hours, and power is delivered more efficiently when the system is not under strain.  So a TES system can freeze water at night, when energy is cheaper, use the stored ice to cool the air during the day, and then return the water back to the tanks at night.

ROI for Thermal Energy Storage

TES allows buildings to shift cooling operations to off-peak hours, thereby reducing peak demand by 20-40%.  It has also been shown to reduce energy costs by 10-20%, and is therefore quickly gaining traction as a must-have design element in new green construction and retrofitting.