Featured article: Prepare your building for the summer cooling season
May 16, 2017
It’s that time of year again, when people get together and enjoy the nice weather outdoors in backyards and light up the grill. You would never think of neglecting refreshments at one of these barbecues; forgetting ice cold beverages.
It would never be a good idea to start making ice as people began walking through the door, right? That would be ludicrous.
Yet that it what we do every day in our buildings. We design the HVAC system to start as people begin to walk through the door. There is no planning involved other than preparing for the biggest cooling load. How often does that happen?
If we did not plan for the actual size of the gathering, there would be a lot of wasted effort and supplies every time. For a party you would need a pound of ice per person but to keep that same person cool the next day in a building would require 150 to 300lbs of ice. Think of the wasted time and energy by not planning.
If we plan ahead for our barbecues, wouldn’t it make sense to plan ahead to cool our buildings too? Planning ahead just takes a little foresight and a special key ingredient – thermal energy storage.
Thermal energy storage stores ice to cool people in buildings. It’s a novel approach to conventional air-conditioning, akin to making ice before the party.
So why isn’t this ice storage cooling standard practice in buildings especially when energy costs two to three times more during the day than at night? Part of the problem is that people don’t like change and many energy consumers just don’t understand their electricity bill and the role peak demand charges play in hiking up energy prices. Those that do know, are outperforming their competitors in energy costs savings.
The energy efficiency myth
What building owners first need to understand is that energy efficiency by itself isn’t enough. Seen as a way to be green and the main way to lower energy costs, efficient energy use reduces the amount of energy required to operate a building. So building owners invest in the most energy efficient lights, chillers, fans, pumps, etc. Still energy bills are higher that they could be because of a little known fact that utilities charge commercial buildings on more than just the total amount of energy use (kWh). In fact, up to 70% of a commercial utility bill is demand related.
Since utility bills can be confusing, this article will break down how demand works and affects operational costs. As in the case of California’s Title 24, the utilities look at when energy is used. They find when the most energy was used during a 15 minute period in the monthly billing cycle. This is the “peak demand” period.
To determine demand (for yourself add up the multiple instances of kW on the utility bill), utilities look at a facility’s peak energy usage. A demand charge is accessed against that peak demand (kW) period. The lower you get this peak demand period, the more you save.(For example, a 300kW peak in energy use times a typical $10 demand charge is $1,000 less per month than 200kW times the same $10 demand charge).
Demand charges may vary by time of day or by season. There’s also coincident peak for a handful of the hottest days of the year.
The reason peak demand is so important to utilities is that the grid must have enough infrastructure to support peak energy use “demand.” Peak demand periods typically occur during hot summer days when people pump up their air-conditioners.
It should come as no surprise then that cooling is largely responsible for high energy prices and that reducing energy use of cooling equipment on hot summer days can dramatically lower operating costs. Likewise, shifting energy use for that cooling can result in tremendous savings especially in large buildings.
Large buildings typically use chiller equipment to provide cooling. Chillers are centrally located, more efficient, last longer and require less maintenance than rooftop and window AC systems. Still chillers can typically consume over 50 percent of the electrical usage.
Another interesting issue affecting the high cost of peak demand is that renewable energy can make energy prices even worse. When power generation is reduced or has stopped, a net zero building (NZB) won’t keep you cool or warm for long unless you have insulation or energy storage.
Most net zero buildings are tied to the grid, however when the sun doesn’t shine a NZB must rely on the grid as back-up, thus the utility must have enough infrastructure to support this request for power. With more buildings using less energy and air-conditioning and renewable energy demand growing utilities must find a path to compensate for all the idle infrastructure that’s so desperately needed. As a result demand charges meant to cover these costs for delivering electricity are on the rise.
Demand charges on the rise
In Boston, businesses pay one of the highest demand charges in the nation. They regularly pay over $45.00/kW (the demand charge) during peak demand hours. The state of Massachusetts is looking to procure more renewable energy and has so launched a bill to facilitate adoption of energy storage on the grid and in buildings. This energy storage legislation will address the reduction of greenhouse gas emissions and peak electrical generation.
Meanwhile, one energy storage system lays quietly nearby in the basement of a federal building. Prepared for high demand charges over a decade ago, the energy storage system according to NPR news is made up of frozen batteries that can be charged when energy is cheap and harvested when cooling is needed.
Planning for tomorrow
Prior to the clean energy movement, demand charges were reserved for just commercial customers. Today, utilities are working on applying demand charges to residential customers as well.
In Chicago, the utility moved to create legislation that would charge residential customers demand charges, saying charging customers based on their highest demand spikes is necessary to adequately cover the cost of keeping up the grid. Midwest Energy News reports that energy providers such as one Arizona cooperative instituted demand charges on all customers with solar. Eversource in Massachusetts and Tucson Electric Power Co. in Arizona is proposing demand charges on solar customers.
Demand charges are on the rise and energy storage systems can keep them at bay. Energy storage systems kick on when energy use spikes. Thermal energy storage systems are proven in over 4,000 installations to allow business to create and store cooling needs at night and then use the stored cooling the next day during the peak demand periods.
Relying on ice in combination with other forms of storage (water heaters, batteries, etc.) minimizes reliance on the utility and supplements renewable resources. It’s like buying ice before the party, just a hundred times smarter. Want to learn more watch this video.
