Communicating Thermostats for Building Retrofit Applications Communicating thermostats create a new potential for old HVAC equipment that would typically be left as-is for the remainder of its useful life.

Casey Birmingham Project Manager The Falcon Group

Communication –missing link in the energy management cycle

As of 2010, the total U.S. building stock was approximately 275 billion square feet^[1], the vast majority of which is regulated by thermostats. Thermostats serve as the most common interface between the occupant and the building systems that control the comfort in the space.  Data from thermostats, when placed in the proper context, can reveal valuable information and insight to a facilities manager. Data such as space temperature and setpoint can be manipulated into informative alerts, prompting the facilities staff to take proper actions to yield tangible energy and cost savings. Data from the results can be used to close the loop in the BEMS process, creating a self-adaptive process that helps to optimize HVAC equipment operating sequences.

 

A truly closed loop energy management system is rarely seen in the built environment, primarily due to the lack of infrastructure in place to collect and transmit data. Many facilities managers perform actions based on their experience and working knowledge of the mechanical equipment in their building. These actions such as adjusting the drive speed on a pump motor or changing the hot water supply temperature setpoint might yield the desired result, but they are usually reactionary changes caused by complaints from building occupants. Local space temperature and comfort data can allow facilities staff to make informed decisions and take a proactive approach to facilities management.

So how can this critical data get acquired in an existing building with occupants, obsolete HVAC equipment and a limited budget? It is not economically feasible to wire existing thermostats to a new centralized building energy management system (BEMS). What about spaces without any thermostatic control? It is prohibitively expensive and disruptive to wire new remote thermostats to existing HVAC terminal devices. Furthermore, older terminal HVAC devices installed prior to the onset of solid state electronics will require either a line voltage thermostat or an additional high voltage relay for proper control.

“Communicating” thermostats is a new term for an old device that performs the same primary function as it did 50 years ago. The critical difference is that unlike traditional thermostats, communicating thermostats can wirelessly send, receive and relay information to other devices. Several manufacturers make battery-powered or self-powered communicating thermostats, creating a completely wireless “peel-and-stick” solution for spaces without an existing remote thermostat. This technology provides a low-cost way to transmit vital data to facilities managers, filling in the missing link in the energy management cycle.

New Potential for Old Equipment

Communicating thermostats create a new potential for old HVAC equipment that would typically be left as-is for the remainder of its useful life. This potential can be realized as an affordable, manageable and scalable retrofit solution for buildings currently without a BEMS or automation system.

Affordable
Labor typically accounts for 50% or more of the total project cost when installing a new thermostat. The costs and inconvenience of cutting drywall, snaking wire, patching new drywall, spackling and painting the wall with primer and finishing paint coats can be avoided with wireless, communicating thermostats. A wireless solution is also highly preferred for most building owners and tenants who wish to implement the most non-invasive solution possible.

Manageable
A communicating thermostat can be managed locally in its respective building zone, centrally on a master controller as part of a BEMS or remotely over the internet via a webpage front end. The versatility of this technology allows for easy and convenient system management from any location with an internet connection.

 

Scalable
Communicating thermostats serve as a highly scalable solution due to their fast, low-cost installation. A building is not a static, but rather a dynamic environment with systems that can change dramatically throughout the building’s lifetime. As building owners renovate, tenants knock down interior walls, or equipment is replaced, the heating and cooling loads in each space will change. Scalable solutions are highly advantageous in this type of dynamic environment. Once the BEMS backbone is in place, additional communicating thermostats can be deployed or moved as the needs of the building change. The versatility of communicating thermostats also allows for a phased deployment, implementing in strategic clusters throughout the building.

Navigating the Jargon

What makes a “communicating” thermostat a communicating thermostat?
Although communicating thermostats perform the same basic function as a traditional thermostat, they are inherently different in how they transmit information. A communicating thermostat has the ability to wirelessly transmit sensory and control information to other devices.

What’s a transmitter? Is it the same as a thermostat?
It is important to recognize the distinction between a thermostat and a transmitter. The key difference is that while the thermostat performs control logic to send signals to an HVAC end device for temperature regulation, a transmitter merely sends the temperature data it receives to a controlling device. There is no embedded logic in a transmitter.

What is a receiver? Is it the same as a controller?
Similar to the transmitter vs. thermostat distinction, a receiver does not have any embedded computational logic to control an HVAC end device. A receiver merely accepts a wireless command signal and performs a function, typically related to a relay. A controller on the other hand comes with either pre-programmed or programmable logic to receive signals, interpret the desired function and pass the desired output to the end device. Do not get stuck with a device that cannot perform the function you had intended because you did not realize receivers are not the same as a controller.

“Wireless” means less wires
The idea of a completely wireless installation is something that engineers and contractors may fantasize about, but it is often not the case. Many communicating thermostats that are listed as “wireless” give the customer the impression that the thermostat is truly a “peel-and-stick” device that requires no wires or power at the wall. This is sometimes true. There are battery powered ZigBee and self-powered Enocean communicating thermostats available that can be mounted on any indoor surface without wires.

Many “wireless” communicating thermostats are only wireless in the sense that they can communicate via radio frequency transmission amongst each other. Most of these thermostats still run on 24 volts and require low voltage control wire to send signals to HVAC end devices. This type of “wireless” communicating thermostat is typically acceptable when replacing an existing thermostat. It is extremely important to make this distinction when installing a new remote communicating thermostat in a space without an existing thermostat.

Wireless Data Transmission – Available Technologies

The advent of communicating thermostats came with new, low-power methods for data transmission. Enocean and ZigBee are the data transmission technologies at the heart of the new wave of building automation devices. Enocean and ZigBee RF transmitters are low-power, low data transmission devices. These characteristics are well suited for building automation devices where wiring is critical and large amounts of data transmission are not typically necessary. Though different, both technologies have key advantages over conventional data transmission technologies such as WiFi or Bluetooth.

Table 1 - Wireless communication technologies, comparison table^[4]

Technology	Com. Standard	Power Consumption	Throughput [Kb/s]	Range [ft]	Frequency
Wifi	IEEE 802.11	High	10,000	30-300	2.4 GHz
Bluetooth	IEEE 802.15.1	Medium	1,000	10-30	2.4 GHz
Zigbee	IEEE 802.15.4	Very Low	250	100-300	2.4 GHz
Enocean	ISO/IEC 14543-3-10	Self-powered	125	30-100	315 or 902 MHz (US) 868 MHz (EU)

Power Consumption
The most important advantage over conventional transmission technologies is the low power consumption associated with both ZigBee and Enocean. ZigBee devices transmit small data packages over a periodic rate, allowing ZigABee devices to run on conventional batteries capable of lasting several years. Enocean devices transmit at a lower data rate and consume even less power than ZigBee. Many Enocean devices are self-powered and capable of harvesting all necessary power for data transmission from small solar cells or mechanical switches.

Common Network Geometries
Wireless communication networks have a variety of possible geometries depending on the functionality of the coordinator and devices. All signals must be passed through the coordinator for the network to function properly. The coordinator serves as a single point of failure for the network, making it extremely important to ensure that the coordinator can withstand power outages and other contingency events. Full function devices are capable of passing data though from one device to another. Reduced function devices can only send and/or receive signals from one source.

 

Enocean devices operate as a point-to-point network as shown in the “star” and “cluster tree” configurations above. Signals are routed over a preconfigured pathway to and from the network coordinator. ZigBee devices operate in a self-healing “mesh” network, routing signals to and from the coordinator through any combination of devices along the way. Typically, a signal can pass through up to 5 devices before signal degradation becomes a problem.  The mesh geometry is advantageous over the star or cluster-tree geometries because it reduces the number of potential points of failure.

ZigBee Family
There are two families of ZigBee devices found in HVAC control equipment, ZigBee Pro and ZigBee IP. The ZigBee Pro family consists of a universal standard, allowing all ZigBee Pro devices to communicate over the 2.4 GHz bandwidth. ZigBee Pro Green, a self-powered version of ZigBee Pro is now available in limited applications. The ZigBee IP family is a collection of proprietary communication protocols, specific to each manufacturer. Typically, ZigBee IP devices must be made by the same manufacturer to communicate. For more information, please refer to the ZigBee Alliance^[2]: http://www.zigbee.org/.

Enocean Alliance
The Enocean Alliance consists of a group of OEMs and distributors who promote and sell Enocean devices. A variety of wireless, self-powered equipment including switches, sensors, controllers, receivers and gateways are provided on the alliance webpage, along with product documentation and links. For more information, please refer to the Enocean Alliance^[3]: http://www.enocean-alliance.org/en/home/.

Major equipment manufacturers

Table 2 - Enocean and Zigbee communicating thermostats – sample of available products as of June 2013

MFR	Model	Communication	Control	Power
Ilumra [5]	SR04	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
Thermokon [6]	SR04	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
Distech [7]	Allure	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
EchoFlex [8]	RTS	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
KMC [9]	STW-6014	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
Siemens [10]	QA96	Enocean 315 MHz	Enocean 315 MHz	Self-Powered
WiSuite [11]	WiStat WR	Zigbee IP	Zigbee IP	Battery
Verve [12]	X41031L0W3VN	Enocean 315 MHz	Wired Line Voltage	Wired
Schneider Electric [13]	Cassia	Zigbee Pro	Wired Line Voltage	Wired
Greenologic/4-noks [14]	ZED-TCMR-M	Zigbee IP	Zigbee IP	Battery
Honeywell [15]	DT92	Zigbee Pro	Zigbee Pro	Battery
Enernet [16]	T9000	Proprietary 900 MHz	Zigbee IP	Battery
Telkonet [17]	EcoWave	Zigbee IP	Zigbee IP	Battery
Viconics [18]	VT7300	Zigbee Pro	Wired 24 VAC	Wired

Table 3 - Enocean and Zigbee gateways - sample of available products as of June 2013

FR	Model	Input	Output	Bidirectional
Thermokon [6]	SRC04-FTT_315	Enocean 315 MHz	LONworks	unknown
Thermokon [6]	SRC65-BACnet_315	Enocean 315 MHz	BACnet IP	unknown
Schneider Electric [13]	MPM-GW2	Enocean 315 MHz Zigbee Pro	Zigbee Pro BACnet	Yes
Viconics [18]	VWG-40	Zigbee Pro	BACnet IP	unknown
Schneider Electric [13]	CSEC01	Zigbee Pro	BACnet IP	unknown

Design Considerations

Understand your project scope
It is important to understand the overall purpose when implementing communicating thermostats. Identify the parties that will be managing these thermostats and whether the thermostats will be managed locally, centrally across the building or remotely over the internet. Once the purpose is established, identify the I/O points (if any) that will comprise the BEMS. How will these I/O points be transmitted between the communicating thermostat and the central management system? Will bidirectional data transmission be required? If so, the communicating thermostat and gateway equipment must be selected accordingly. Is the BEMS going to integrate with other control systems in the central plant? If so, the gateway will likely have to convert thermostat I/O points into a conventional protocol such as BACnet, Modbus or LONworks.

Additionally, it is important to understand the existing conditions within each space to be controlled. There are an infinite number of potential existing conditions, however many can be categorized into one of the three conditions below:

 

Equipment limitations
Before developing detailed engineering plans and specifications, it is a good idea to verify wireless transmission ranges in the field with a signal strength indicator. Ranges provided in manufacturer specifications are general guidelines and vary substantially from building to building. Metallic surfaces such as metal studs, elevators, or decorative hallway finishes can partially or completely block signal from passing through, so field verification is extremely important.

Another important consideration is how each device will be powered, especially in the built environment where additional wires and electrical raceways are not always acceptable. Providing power, configuring communications between each thermostat, end device and gateway quickly add labor costs to the BEMS. All of these factors must be considered when budgeting for a project, laying out floor plans and selecting equipment.

When selecting equipment, is it critical to understand the operating sequence of each HVAC end device and how the device will be controlled with your communicating thermostat. Understand which piece of equipment will house the control logic in the operating sequence. If a relay is only configured to communicate with a specific thermostat or temperature sensor, make sure that the sensor has the control logic, either pre-programmed or programmable, to carry out the proper operating sequence.

[an error occurred while processing this directive] Industry trends and projections

Communicating thermostats have made substantial advances since their inception, including gains in wireless range, increased reliability and battery life improvements. The industry has grown in a unified manner, allowing for more comprehensive solutions as products become more compatible with one another. Major manufacturers have joined the party, most recently noted by Schneider Electric’s acquisition of SCL Elements, the makers of Can2go in January.

Enocean is in the process transitioning from the original 315 MHz North American frequency to 902 MHz. The new North American frequency is supposed to increase the wireless range by a factor of 2 or 3. Manufacturers are silent on the exactly how improved the new transmission range will be. Expect the new frequency to be available on existing products by Q4 of this year.

ZigBee Pro Green, the first self-powered ZigBee device, is currently available in limited applications such as wall switches. This technology will continue to grow into many of the self-powered applications currently served by Enocean. It will likely be some time before wireless, self-powered ZigBee thermostats are readily available on the market. For more information, please refer to the ZigBee Alliance: http://www.zigbee.org/Specifications/ZigBee/GreenPower.aspx.

Communicating thermostats will continue to grow in sophistication in the coming years. Touch screen user interfaces such as the one made by Nest^[19] are becoming more prevalent on high-end thermostats.

 
References

[1]    http://architecture2030.org
[2]    http://www.zigbee.org/
[3]    http://www.enocean-alliance.org/en/home/
[4]    http://www.csr.com/sites/default/files/white-papers/comparisons_between_low_power_wireless_technologies.pdf
[5]    http://www.illumra.com/
[6]    http://www.thermokon.de/EN/thermokon-sensortechnik-14/start.html
[7]    http://www.distech-controls.com/
[8]    http://echoflexsolutions.com/
[9]    http://www.kmccontrols.com/
[10]   http://w3.usa.siemens.com/BUILDINGTECHNOLOGIES/US/EN/
[11]   http://wisuite.com/
[12]   http://www.vervelivingsystems.com/
[13]   http://www.schneider-electric.com/site/home/index.cfm/us/
[14]   http://www.greenologic.co.uk/
[15]   http://honeywell.com/Pages/Home.aspx
[16]   http://enernetcorp.com/
[17]   http://www.telkonet.com/home/
[18]   http://www.viconics.com/
[19]   http://nest.com/
 

About the Author

Casey Birmingham, Project Manager – The Falcon Group

Mr. Birmingham is a Project Manager with the Energy/MEP division at the Falcon Group, specializing in energy audits, energy monitoring and visualization and building operations.

He has designed and installed a low-cost energy monitoring and visualization system for the Falcon Group’s Headquarters office in Bridgewater, NJ. The system tabulates minute by minute electric and natural gas data and provides results and recommendations based on weather-correcting factors.

Mr. Birmingham and the Energy/MEP division have led a variety of EERE building retrofit projects over the past year months, including the conceptualization and design of a building energy management system (BEMS) as part of the New Jersey Pay for Performance program. The BEMS will utilize data from communicating thermostats for optimized control of the building’s boilers, chiller and VFD drives. When complete, the project will reduce the building’s site energy consumption by over 40%, saving over $380,000 in annual operations costs.

He is a graduate of Northeastern University and holds a Bachelor’s Degree in Mechanical Engineering.  He currently holds his Engineer in Training (EIT) certificate and is pursuing a professional engineering license.  He is a member of the American Society of Heating Refrigeration and Air Conditioning Engineering (ASHRAE).  He has completed coursework provided by ASHRAE in both HVAC and HVAC controls. This is Mr. Birmingham’s first contribution to AutomatedBuildings.com.

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