Articles and whitepapers

Going Green: Tying Energy Savings to Building Automation (5/1/2012)

By Adam VanOort, DataNab

The goal of energy conservation in the home moves closer to mainstream acceptance as green technology evolves. For many, the thirst is present, but obstacles remain when it comes to cost and implementation.

Concepts such as load shedding and load shifting are growing in popularity here in the United States, particularly in the southwest where populations lean heavily on daytime air conditioning.

Regardless of region, all indications point to power getting more expensive. This is bound to bring further attention to energy-saving techniques such as load shifting across the nation, as well as internationally.

Regardless of region, power is getting more expensive.

Staying efficient

Load shedding offers a way to turn electric currents on and off as a home or building owner reaches a demand limit, eliminating potential penalties. Load shifting meanwhile offers ways to use energy at different times of the day. This ensures that air conditioners, lights and other energy-consuming devices don't have to always be shut down during peak times.

Building automation is an ideal way for homeowners and landlords to tie load shedding or load shifting operations into the picture. Building automation systems, comprised of a series of programmable controllers, sensors, intuitive software and other components, can essentially drive these efforts for the user through automated processes and alerts.

Home automation can be integrated with energy-consuming devices and load shedding systems.

Building automation has progressed to the point where many users have moved onto the IP layer. IP technologies give facility owners and managers the flexibility to migrate from legacy systems that locked them into specialised, proprietary systems, in favour of scalable systems with open standards.

The IP environment, or smart grid, also allows users to take advantage of an existing network infrastructure. This not only does away with bundles of wires that are difficult to manage, but also creates a universal pipe to connect multiple systems and equipment components. It also provides an ideal platform to monitor operations and collect important data including run times and energy consumption.

How it works

Load shedding systems typically rely on utility companies triggering a closed relay to communicate load shed requests over the internet to building automation systems. The relay ideally communicates with any number of open-standard controllers connected to the facility's network infrastructure to begin the process. Those controllers internally de-energise the relays to shed loads, and potentially communicate with sub-controllers within more complex, multi-layer building automation systems to drill deeper.

IP controllers and sub-controllers act as the bridge devices between the network infrastructure and the systems and machines that power the building. This typically includes lights, HVAC units, chillers, boilers and/or water pressure systems. Controllers with the appropriate I/O connections can also bring components tied to security, life safety and even AV systems onto the network. This might include digital and analogue cameras, fire alarm panels and temperature sensors.

A typical building automation system will have at least one central I/O component, with relays enabled on the output to turn machines and other building systems on and off. In larger dwelling units, such as apartment buildings, sub-controllers allow integrators and end-users to bring more devices onto the network. This connectivity essentially enables a smart infrastructure to support load shedding, based on a series of controller and sub-controllers with multiple relays programmed to turn systems in specific zones on and off at specific times.

A unique perspective

Power costs are highest during peak times of the day when energy usage is maxed out. The theory behind load shifting is to use more power when it's cheap and less power when it's expensive. The challenge is finding a load shifting solution that will keep fully-occupied homes and buildings comfortable as temperatures surpass 80, 90, or even 100F degrees.

One solution is to run the air conditioners at maximum output through the morning and dial back during the peak afternoon hours - and deal with the tremendous downsides. It's terribly inefficient, and creates an environment where everyone is cold in the morning and becomes gradually hotter throughout the afternoon.

A better solution is to store cooling energy for use at a later time. Using thermal storage, building owners can create cooling energy at night or in the morning when temperatures are low and power is cheap, and store that cooling energy for use during the hotter peak demand periods. This would allow homes and facilities to turn off air conditioning when rates are most expensive.

How do we get there?

The proof of concept for thermal storage exists today at the author's home near the Twin Cities of Minneapolis and St. Paul, Minnesota. The overall solution essentially merges home automation with load shifting - but with a unique twist.

My concept uses the free cooling potential from the home's water supply to charge a thermal battery, which stores cooling energy for on-demand use, and/or replace the cooling provided by the air conditioner. The thermal battery is powered with a phase change material (PCM) rather than water. Water has a very low freezing point (32F degrees), among other negative attributes that complicate the process.

The thermal battery concept for cooling purposes.

The solution was to find a substance that could store thermal energy in my thermal battery, with a higher 'freezing' point to convert from liquid to solid phase using only the average temperature of my home's water supply as the cooling mechanism. This made it possible to take advantage of the additional energy storage capacities that exist when a substance changes phases from liquid to solid - and also store a large amount of energy in the thermal battery, at a temperature which would cool the home.

HTF Exotherm technology helped achieve this goal. HTF Exotherm is an unusual PCM: exceptionally stable, non-caustic/toxic, and capable of storing and releasing large amounts of energy. It doesn't have to be 'encapsulated' to protect ancillary equipment and is capable of transitioning back and forth from solid to liquid a virtually unlimited number of times without degrading.

The HTF Exotherm PCM can be formulated to target a specific transitional temperature where the material changes phase from liquid to solid. This made it possible fill a thermal battery tank with a specific HTF formulation designed to freeze at 60F, and successfully charge by using only the cooling energy available through the incoming household water supply.

System design

The system design is rather simple, comprising of an insulated holding tank, some piping, two small pumps, a collection of sensors and coils, and a couple of controllers, with a tank of specific-temperature HTF Exotherm PCM at its core.

The thermal storage system.

Water enters my home at approximately 55F degrees, with slight fluctuations depending on the time of year. The water first enters the insulated holding tank and then proceeds to a 150-quart thermal battery tank containing the PCM. The water then circulates through a copper coil inside of the tank which enables heat transfer between the water and the PCM.

Free cooling energy is captured from the water supply and stored in the thermal battery prior to the water going through the home. This enables the storage of free cooling potential for later use rather than wasting it as cold water runs down a drain or is spread across a lawn.

The purpose of the holding tank is to circulate water through the thermal battery even if there is no water flowing to the home. Without the holding tank, there is only one chance to capture cooling energy from the water. With it, it is possible to circulate the cold water in the tank through the thermal battery multiple times until all of the available cooling potential is extracted from the water.

On the other side of the tank, liquid circulates through another copper coil and sent to a cooling coil in the supply ductwork. Air is cooled as it passes through this coil, helping to cool the home with extremely minimal costs. The only associated cost is the tiny amount of power required by the two small pumps to circulate the fluid from the tank up through the cooling coil in the ductwork, and to circulate water from the holding tank through the coils in the thermal battery.

The water leaving the tank and going out to the house is warmer since the PCM has captured cooling energy from it and stored it in the thermal battery. The benefit is twofold:

* Cooling energy from the water supply is now helping to cool the home.

* The amount of work traditionally required by the hot water heater to heat water for showers and other purposes has been reduced.

Control and automation

The complete system incorporates a variety of control and automation components to assist with the general operation and real-time monitoring.

DataNab temperature sensors are positioned throughout the system. Two sensors measure primary incoming and outgoing water supply temperature. Using these sensors, along with an associated flow meter, we can determine how much energy is captured as the water moves through the tank and out to the home.

Additional DataNab sensors note the tank temperature, providing clarity on when the PCM material is fully frozen - and therefore fully charged. More sensors on the outbound side of the tank offer detail on water temperature as it moves through the air duct and exits at a warmer temperature. This provides insight into how much energy is transferred to the air circulating into the home.

Other sensors in the system include:

* Sensors upstream and downstream of the cooling coil in the supply air duct, which displays how much the air is cooled as it is circulated through the home.

* A room temperature sensor and an outdoor air temperature sensor to help decide when the system should run.

All of these sensors provide comparisons between various points, and determine how much the home has been cooled using the system.

Most of the sensors are run direct to a DataNab MBus_Io10_LCD programmable controller, which has a built-in LCD screen and buttons to scroll through connected sensors, displaying water-in temperature, water-out temperature, tank water temperature, cooling coil temperature and so on. The various readings can automatically flash across the screen one at a time, providing a simple monitoring solution without the need for a computer. Set points and modes can be changed from this interface, controlling when the system will run.

A Barix Barionet controller picks up some additional sensors (the MBus_Io10_LCD supports eight external sensors) and talks to a WattNode demand meter, which provides data on electrical power demand and consumption used by the system. The Barionet can collect data from the WattNode and the other temperature sensors and deliver it the LCD screen of the MBus_Io10_LCD for local monitoring purposes.

The control system including DataNab MBus_Io10_LCD programmable controller and Barix Barionet controller.

The Barionet offers a built-in web server to display all of the associated data via a webpage - essentially IP-enabling the entire system. It also allows me to enable and disable the system via the web, and delivers alarms via email if the system isn't functioning properly.

The overall system costs are quite low. The insulated holding tank is just a re-used water heater tank, and the thermal battery tank is a store-bought cooler priced at US$80. The off-the-shelf copper coils were priced at US$20 a piece, and the small circulating pumps each cost around US$50. The total cost of the sensors, the Barionet, and the MBus_Io10_LCD is under US$350. The WattNode demand meter and the water meter are optional components and economically priced.

Commercial applications

Larger apartment buildings can implement the same design on a wider scale, with the number and size of pumps and tank size to be determined by the cooling load and complexity of the facility; and the integration of more controllers, sub-controllers and relay units as necessary to automate processes.

There are essentially two ways to charge the central thermal battery tank in a commercial application of this system.

The first option is to tie the operation to an actual geothermal system. This would provide a dedicated process for circulating water underground for natural cooling, and then bringing it back through a coil in the tank to charge the phase change material. This could be an adequate solution to charge the tank, depending on the temperature of the ground loop and the cooling requirements of the building.

A second option is to run AC compressor coils through the tank to charge/freeze the substance. Large commercial spaces may require that the tank temperature be as low as 45 degrees to properly cool the building during peak hours. This would require running compressors at night or during off-peak hours to fully charge the tank, when the exterior air is cooler, power is cheap, and the compressors don't need to work quite as hard.

The overall concept is to charge the tank at the most efficient possible times. The energy can then be stored inside the thermal battery for use during peak demand periods, keeping the facility safe from high demand penalties and saving the owner money.

Tying this back to central control devices like the Barionet will assist in data aggregation pertinent to the operation. The number of controllers required is typically tied to the density of the system - the higher the I/O point count, the more controllers that are needed to compile and record the information. Centralised software will further provide the operator a bird's eye view of every controller and sub-controller in the network, which is helpful to pinpoint service issues, troubleshoot and respond accordingly.

Conclusion

Tying power and energy saving efforts to building automation has never been easier. The flexibility of the many tools and devices available allow virtually any homeowner or building owner to build a manageable an effective system that matches their budget.

Adam VanOort is President of DataNab, provider of cost-effective IP-enabled solutions for audio distribution, process controls, energy management, building automation, remote monitoring, data acquisition, security and access control and other related applications.

www.datanab.com