A solid data model for interoperability must be presented to this community before we will realize the growth potential we have. Interoperability must not only exist between our home products and us, it must also exist between the products themselves; each product enhancing the feature set and functionality of the other.

Home Plug & Play

Brian Baker

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Brian Baker

A solid data model for interoperability must be presented to this community before we will realize the growth potential we have. Interoperability must not only exist between our home products and us, it must also exist between the products themselves; each product enhancing the feature set and functionality of the other.

This column will typically be dedicated to providing information about how you can utilize concepts presented in the Home Plug & Play specification to build a network of products having a high degree of interoperability. The Home Plug & Play Specification development and the Common Application Language have both been decoupled from the CEBus protocol. This enables them both to move ahead and work toward the goal of protocol independence. The first Home Plug & Play products out of the gate will most likely operate on a CEBus protocol stack.

One of the things that this industry has needed for a long time is a data model for interoperability of products within the home. The home network is a strange beast. Up until now, communication in this home network has mostly been limited to simple on/off control commands. No one has really stepped forward and offered the industry a model to be used for understanding how products in the home could/should interoperate amongst themselves. The approach up until now has been to assume that only we humans will want to interoperate with a given product. For a long time, no vision of an intelligent homogeneous network of consumer electronic products was presented to this community. Much of the equipment available on the market for us to use in building home automation systems has been developed in such a manner as to perpetuate the absence of vision. This immature market wined and fussed, demanding a more convenient means for human control of home products. Like a hungry child with her nose pressed against the pastry cabinet window of a grocery store, we begged and pleaded for what looked the most appetizing. The market did not know what else to ask for; it just knew it was hungry for something. Some manufactures have capitalized on this situation and offered quick-fix solutions under the guise of being "market driven". They focused more on building an empire by gadgetizing the industry rather than taking a leadership role in guiding the industry in the right direction. In my opinion, this lack of vision is directly responsible for the snail pace in growth this industry has experienced.

A solid data model for interoperability must be presented to this community before we will realize the growth potential we have. Interoperability must not only exist between our home products and us, it must also exist between the products themselves; each product enhancing the feature set and functionality of the other. I believe the CEBus Industry Council is on the right track with the Home Plug & Play Specification and the interoperability model presented therein. Over the next few months I hope to provide you with insight into the vision of interoperability that has been captured within the pages of this specification.

 HVAC and Energy Conservation

I am curious about what sort of folk visit this web site. I don't suppose we represent your "average k-mart shopper"; so to speak. Nonetheless, we represent a unique, and yet very real, segment of today's society. The fact that we use our computer to research information concerning home automation puts us close to what the youth of today might call "the geek zone". However, I expect one day we can all say proudly that we were home automation before home automation was "cool". I will assume that a fair number of you are not experts in home automation and that most of you are not all-knowing when it comes to Energy Conservation. I don’t pretend to be an expert in either field, but in the last 20 years or so I have come across some bits and pieces of information you may find helpful, or at least a bit interesting.

This rest of this article will not discuss Home Plug & Play. Instead, I will try to provide some insight to some of you who are not familiar with the legacy of energy management systems that focus on the HVAC system for energy conservation and cost savings.

About a month or so ago my wife and I decided it was about time to put a new roof on our house. My wife knew that a new roof was way overdue but I didn't become convinced until a section of drywall became "wet-wall" after a heavy rain. In preparation for the roofers, I decided to remove two solar panels that had been installed about 20 years ago; well before we purchased the home. These panels had not been in use for most of the past ten years. I live in the desert southwest where, around about the time these panels were installed by the previous owner, solar panels were the "in thing". I remember the time well. It seemed as though everyone and their brother was having solar panels installed on their rooftops in an effort to reduce their domestic water heating bills and take advantage of the generous tax incentives that the government had put in place. As I carefully dropped each of the large rectangular collectors over the side of the house to the ground below, I was reminded of the thoughts of King Solomon captured in writing thousands of years ago:

"To every thing there is a season, and a time to every purpose under the heaven: a time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted; a time to kill, and a time to heal; a time to break down, and a time to build up; a time to weep, and a time to laugh; a time to mourn, and a time to dance; a time to cast away stones, and a time to gather stones together; a time to embrace, and a time to refrain from embracing; a time to get, and a time to lose; a time to keep, and a time to cast away; a time to rend, and a time to sew; a time to keep silence, and a time to speak; a time to love, and a time to hate; a time of war, and a time of peace. "

The truth be known, the solar panels that I removed from my roof are fully functional. In fact, they showed little signs of aging after 20 years. However, it cost more money to run the electric pump to circulate water through the panels than it costs for me to heat the water using a natural-gas-fired domestic water heater. If I could transport myself back in time, bringing the panels with me, they would be worth about $5000.00 apiece; as is. But today, there is no oil embargo. There is little financial incentive for using this form of energy conservation technology today; at least here in the southwest. I suppose that a few very enterprising fellows acquired a significant chunk of wealth installing these things years ago. However, there was more to be said about the nifty technology than there was about how much money it actually saved.

About 20 years ago, when rooftops of homes throughout this part of the country began to sprout these solar panels, another form of energy conservation was gaining in popularity. Unlike solar domestic water heating of that time, this other means of energy conservation still has significant value today. I am referring to computer-based management of HVAC systems.

What is my electricity really costing me?

Some of you may already be aware that commercial and industrial customers of an electric utility are billed very differently than most of the residential accounts. I admit that this situation is beginning to change somewhat across the USA. However, in many parts of the country a residential customer is still charged a flat rate. For those of you who don't know there is a difference or are not sure what the difference is, I will attempt to summarize it here:

While most residential rates are fixed at X cents per kilowatt-hour. Commercial accounts are billed at a rate that is a very small fraction of X. Therefore, all else being equal, if a residential customer and a commercial customer used 100 kilowatt-hours of electricity during the billing cycle, the residential customer might pay 5 times (or more) than the commercial customer for the same usage of the electric utility. The residential customer in our example can demand any level of power for any length of time during his billing cycle and he still pays the same rate.

Things aren't quite as simple for the average commercial customer. A significant portion of their electric bill is calculated in a section on the bill typically labeled demand charge. No such section appears on our residential customer's bill. The demand charge is based on a rate of Y dollars per kilowatt of electric demand. Note that the units of measure are kilowatts for the demand charge while usage is measured in kilowatt-hours. The usage charge is based on power consumption over the time of the entire billing cycle. Demand is measured over a relatively much smaller period (or window) of time. This window can range from near instantaneous to thirty minutes or more. A typical value might be about fifteen minutes. The value of Y can be $15.00 or higher.

There is another interesting twist to the demand charge of a commercial customer. Many utilities use a ratchet billing system that places a minimum value on what they will charge each month. This minimum value is based on the highest measured demand recorded over the past twelve months. This minimum value is typically a percentage of the highest value measured and can be equal to 75 % (or more)of the recorded peak value. This means that a high peak demand recorded in August caused by heavy use of refrigerated cooling during a heat spell, could elevate December's, January's, February's and March's demand charge above the actual measured demand for each of those months.

If you happen to have authorized access to the billing history of a commercial or industrial electric utility account, look for this demand figure on the electric bills received for this account over the past twelve months. Watch for identifiers such as actual measured demand and billed demand. If the utility customer uses refrigerated-air cooling and natural gas heating and the summers are typically hot and long, prepare yourself for a shock. The bills for the winter months may reveal that the ratchet billing system is elevating the electric utility cost for these months far above the actual usage. Depending on how the account utilizes the electric service, the demand portion could be over 50% of the electric bill.

 Energy Savings Through Compressor Cycling

One of the most significant portions of energy demand for a commercial customer is realized when refrigerated-air cooling systems attempt to maintain a comfortable temperature in the building during the summer months. Many cooling systems use refrigeration systems to draw the heat out of the air inside of the building. The compressor unit of these systems is responsible for a significant portion of their power demand. When multiple HVAC systems exist at a commercial site, they can significantly increase the measured demand charge if they are permitted to operate concurrently. This cost can be magnified if the inside temperature of the building is permitted to rise to a high level during off-hours; such as over the weekend. The increased air temperature present when the system tries later to bring the air back to a comfortable temperature causes a double whammy effect. First, the elevated temperature almost guarantees that all the cooling units will run for an extended period of time. This will likely occur for period of time that exceeds the window used in measuring demand. Not only that, but the elevated temperature causes the second-stage cooling compressors to kick in along with the first-stage compressors. Typically, only the fist stage compressor is necessary to maintain the desired temperature. The second stage is provided for severe weather situations where an extra boost of cooling capacity is needed. When these second-stage units kick in to operation, they effectively double the power demand for the HVAC system.

Cycling of the compressor units in large HVAC systems can help reduce the impact these units have on the power demand. Depending on the installation, this can have a dramatic effect on the energy costs during summer months. Because of the ratchet system described above, reduction can carry on into the winter months as well.

I was personally involved in an installation where automated cycling was retrofitted in an existing set of large refrigerated-air cooling systems at a church's building complex. Yes, churches are considered to be commercial accounts. So all you deacons out there should take a close look at your electric utility bills over the past few years. In this particular church, we installed an embedded computer system that was programmed to cycle off the compressors of all of the refrigerated-air cooling units for 10 minutes after 20 minutes of operation. This on/off cycle would repeat as long as the thermostat controlling the compressor was calling for cold air. The local electric utility provider was using a 30-minute window of time for measuring demand back when this system was installed. The computer’s program effectively guaranteed that each compressor would be off for 33 percent of the demand measurement period. To even out the demand of all of the cooling units, we staggered the period of time during which each system’s compressor was operating relative to the others. To help maintain comfort while the compressor was cycled off, the computer would only break the control circuit of the compressor itself. The ventilation fan for the system would remain on if the thermostat was calling for cool air. The moving air helps maintain comfort for the building occupants during this period where the compressor is shut down. The control contacts were placed in series with the thermostat control of the compressor so that the thermostat continued to control the ventilation fan and compressor based on its temperature control operation.

Previous to our installation of this system, the deacon of the church would arrive an hour before Sunday morning service and turn down all of the thermostats from a manual setback temperature of 80+ degrees. This would result in an hour or so of continuous operation of all cooling units; including the second-stage compressors. Since the sanctuary was only occupied on Sunday morning, Sunday evening and Wednesday evening, the actual electric usage indicated on the utility bill was was not significant. However, the demand charge was sky high. With the system installed, the deacon no longer had to arrive to set the thermostats. At 4:00 a.m. on Sunday morning, the system would apply power to the main control thermostats, enabling them to operate. A separate setback thermostat controlled the temperature during off-hours. Compressor cycling would continue as long as the thermostats were powered up. The early-morning start-up of the cooling system enabled it to run without the need for kicking in the second-stage compressors. The automated control system denied control of the second-stage compressors by the thermostat. The cooling units were more efficient in the very early morning hours since outside air is used to remove heat from the refrigerant in the system by passing it over the condenser coils. Cooler outside temperatures enabled faster dissipation of heat by the condenser unit.

In the example installation above, the church realized an $800.00 per month saving on their electric utility bill.

Today we have thermostats that will do a lot of the functions that the computer system did for this church years ago. However, the day will come, probably sooner than you think, when these thermostats will also have the ability to communicate amongst themselves and coordinate leveling out of the electric demand of a building. A Honeywell HVAC system on the north side of a building will voluntarily yield up its compressor’s operating time to a TRANE HVAC system on the south side. This will be possible because of the data model I mentioned in the beginning of this article. Not only will these two systems from different manufacturers be aware of each other’s presence on the network, but they will also be able to exchange information. This information exchange will enable the system on the south side of the building to inform other units that it is having trouble keeping up with the afternoon sun. The unit on the north side, not having run its compressor for the past 10 minutes, will be able to inform the struggling unit that it can engage its second-stage compressors to help it cool things down. Working in concert, these systems will be able to maximize occupant comfort while leveling out demand on the electric utility. Gadget technology won't have much to contribute to this scenario or many of the other complex scenarios that will present themselves in the future.

Updated Biography Mar/03 - Brian Baker is a software engineer at Raytheon Missile Systems located in Tucson Arizona. He was a contributing member of multiple committees and working groups of the CEBus Industry Council while employed at Smart Corporation previous to his joining Raytheon. His background includes development of home automation subsystems and over 15 years of embedded systems development in the defense industry. He was a core member of the developers of the Home Plug and Play specification. Brian can be reached at bdbaker@raytheon.com

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