FIGURE 1. Benefit of self-powered wireless sensors.

Energy inefficiencies in buildings are easy to spot. Less evident, however, are cost-effective means that can remedy the pervasive wastes of energy.

A building owner can easily document a building’s faults and then ask the contractor to propose an energy-efficient solution. Building owners must then weigh the benefits of modernizing the building versus their own fiduciary goals. Building owners often elect to continue to feed an energy-hungry building more power rather than pay the cost of installing a new system.

Fortunately, green technologies have matured. Thanks to innovative engineering and premiums paid by early adapters, contractors can now present cost-effective and field-tested solutions to prospective clients. Products, such as peel-and-stick sensors, simplify and expedite system integration; while providing the building owner a wireless sensor network that yields greater control of building space.

Case studies show that after a reliable wireless sensor network is put into place, energy consumption is reduced. And, over time, building owners recoup the initial cost of installation. (See Figure 1, benefit of self-powered wireless sensors.)

Practical experience has demonstrated that there is a 10 to 60 percent saving potential for amortizations between two and 10 years. In the case studies referenced in this article, energy consumption was reduced 40 percent by implementing green strategies, such as “need-based” heating and cooling. As the studies will document, a network of peel-and-stick sensors can have a positive impact on the environment and on finances.

The wireless networks in this article make use of self-powered wireless sensors and switches that are enabled by EnOcean RF (radio frequency) modules and energy harvesters. The embedded modules enable wireless thermostats, window sensors, and key card switches to operate without batteries or wired power sources.

The energy harvester converts environmental energy (in these cases, solar and mechanical energy) into transmit power that the sensors can use to convey information to HVAC controllers. The self-powered wireless technology is what differentiates the wireless sensor networks in this article from others. (See Figure 2, EnOcean RF modules and energy harvesters.)

FIGURE 2. Example of EnOcean RF Modules and Energy Harvesters.


Let’s study a few case studies. In the case of University of Canterbury, a learning institution in New Zealand, the school wanted to improve the quality and capacity of older dormitory buildings. Modernization of the buildings had to satisfy the following requirements:

• reduce energy consumption and utility spending;

• avoid reliance upon batteries; and

• the installation of sensors could not be invasive, as building closures had to be kept to a minimum.

The solution, in this example, was to install self-powered wireless window sensors (solar-powered magnetic contacts), thermostats, and controllers in each room. The window sensors enable status monitoring of windows. When a window is closed and a room is below a specified temperature, the heating unit turns on automatically. If either the temperature gets too warm or a window is opened while the heating is on, the heating is automatically turned off.

The self-powered wireless controls rendered time-consumptive labors, such as wiring or chiseling conduits unnecessary. (See Figure 3, college dormitory renovation.)

FIGURE 3. College dormitory renovation.


In a different example, a contractor was investigating ways to renovate and modernize a 200-room hotel in Orlando, Fla., plus reduce the amount of energy the hotel consumes. The hospitality building upgrade needed to satisfy the following requirements:

• reduce energy consumption in unoccupied rooms;

• avoid reliance upon batteries;

• maintain and improve hotel guests’ experience; and

• install the sensors and switches in a non-invasive manner. In other words, the hotel had to stay open for business during installations.

The contractor proposed to install self-powered wireless hotel key switches in each room. The key card switch is an EnOcean-enabled wireless transmitter recently developed by Echoflex Solutions. The key switch operates without batteries and solves the problem of heating, cooling, and lighting unoccupied hotel rooms.

The self-powered wireless key card switch acts as a master switch. When a guest enters a room, they insert their hotel key into a lighted dock. When the key card is inserted, a radio signal is transmitted that enables the room’s lights, electronics, heater, and air conditioner. When the key card is removed from its dock, another radio signal is sent that, after allowing the guest 10 minutes to depart, disables the room’s powered amenities.

In the scenario cited here, the hotel owner will make back the initial installation cost in 3.75 years and then pocket nearly $310,000 in net profits during the lifetime of the self-powered wireless sensors and switches, based on 20 years of maintenance-free operations. (See Figure 4, conserving power in unoccupied hotel rooms.)

FIGURE 4. Conserving power in unoccupied hotel rooms.


The following outlines how the savings of $19,045/year was figured:

1.Calculate the amount of power one hotel room consumes in one hour. In this case, the sum of energy consumption per room was 1,080 Watts.

1080 Watts = 750 Watts + 180 Watts + 150 Watts

(• Heater/Air conditioner = 750 Watts;

• three 60-Watt light bulbs = 180 Watts

• TV = 150 Watts)

2.Now multiply the following variables: Power usage (in kilowatts); number of rooms; number of hours room is left unoccupied; hotel occupancy percentage; percentage of guests that leave utilities on when they are not in the room; cost of electricity; and number of days in a year.

After multiplying the variables, the potential energy savings for one year is $19,045.

$19,045 = 1.08 kW x 200 rooms x 5 hours x 70% occupancy x 70% of guests leave utilities on when departed x $0.0986 kWh x 365 days


Installing a self-powered wireless network requires some clairvoyance. If an integrator can see beyond the glare of initial installation costs, long-term gains are in store. Contractors and building owners now have access to products that protect the environment, preserve natural resources and stimulate economic growth.

The benefits of self-powered wireless solutions also stretch beyond the scope outlined in these case studies. No attempt was made to attach a monetary value to other tangibles, such as the costs of battery-replacement. The green solutions cited in this article are not only good for the environment; self-powered wireless controls are also good for business.

Publication date:03/03/2008