One of the most effective energy management strategies is using the lowest cost energy whenever you can get it. The vast population of general use buildings consumes the bulk of energy during business hours when utility companies have variable rates often coupled with demand charges. We are always looking for ways to reduce costs; one common way is to exploit time of day billing by utilizing as much equipment during off peak times (generally at night). Keeping a facility cool during the summer months can be the most expensive time of year, even with implementing economizers. Implementing energy management systems has become commonplace; the return on investment for optimized HVAC loads is rapidly becoming a necessity in order to reduce operational costs. One of the key elements missing from the building environment is energy storage. Venture capitalists have been investing billions of dollars in energy storage for a variety of markets. The big hope for building energy storage is to store those inexpensive midnight kilowatt hours and infuse them in the local building microgrid during daily peak rate times in order to reduce that monthly energy bill.
Alas, energy storage in the form of an economical microgrid size battery remains an elusive animal. I am hopeful this will change someday and economical building battery storage will be a reality. Meanwhile, if electricity is used to cool a building, it is more efficient to store that cooling than an electron on the grid at peak rates to create the cooling. Electricity is not the only form of energy that can be stored; there are good solutions for storing thermal energy for a facility that have been around for years. For the cooling season, CALMAC has an interesting solution called Icebank that time shifts the use of energy by using low cost nightly (off peak) rates to cool and store energy to be used during costly daylight hours. In order to understand the value of time shifting energy, we need to understand how the utility charges for time of day coupled with demand charges. Depending on your location, you are most likely paying two to three times more for electricity due to these demand charges.
Most utilities operate differently, however nearly all have some form of a demand or time of use penalty for consuming energy during peak demand times. The basic definition of a demand charge is the highest peak demand in kilowatts (kW, as a rate, not a unit of time) over the period of a month. These measurements are typically taken at 15 minute intervals and can be unforgiving. The demand charge is determined by the highest peak kilowatt (kW) measured. For example, one building I worked with had a typical monthly demand charge based on the highest monthly measurement, around 225 kW during the summer months. In my area, the demand charge is roughly $9, so the monthly demand charge was roughly $2,025. That 15 minute incremental measurement can be unforgiving; if you average 100 kilowatts as a rate, then for one instance the demand shot up to 225 kW, you pay the monthly demand charge for the entire month based on the 225 kW peak demand measurement. In addition to the demand charge, a utility may also double up on the demand charge with a facilities charge, which is nearly the same measurement, except it may use the highest peak demand measurement to charge you for more than a month. The goal is to lower the overall energy use and limit peak use. In order to do that, you need an intelligent energy ballast.
Storing energy during nightly off peak rate times is one of the easiest ways to reduce the overall costs, but that requires an intelligent energy storage solution. CALMAC’s Icebank system was engineered to take advantage of off peak electrical rates by storing large amounts of ice, then using it during peak times. There are other thermal solutions out there that can store a thermal load at low temperatures, but those are typically at 45 degrees. Icebank stores water at 32 degrees to provide a lower delta-T. Simply put, the delta-T is the difference between two temperatures, and for an HVAC system it’s generally the difference between the current air temperature and the temperature of the HVAC system. I am oversimplifying here, but the greater the difference in temperature, the more effectively you can change the temperature of the ambient air in a building.
In a case study with the University of Arizona the delta T is not the main driver. Icebank stores water at a frozen 32 degrees to take advantage of the latent heat property of water. More btu’s can be stored in a smaller space saving valuable real estate. Since the ice is already at 32 degrees, some designers choose to use those cold temperatures to send colder btu’s with less system flow, be it chilled fluid or air. That reduces pumping horsepower saving even more money in addition to new designs lowering cost with smaller fans and ductwork.
The ice storage implementation at the University is saving a significant amount of energy costs by enabling low cost energy storage to be discharged during peak periods, but also to assist in load optimization with the existing combined heat and power system. Icebank energy storage and the chiller operations are synced with turbine operation to optimize energy output from the turbine. According to former Sr. Staff Technician Marianne Deutsch, “Shaving this peak represents up to a $38,000 monthly savings to the University”.
For urban areas, Icebank is best implemented in buildings 500K sq feet and larger. K-12 schools and places of worship with short duration low load factors are great candidates for storage too in both urban and less populated areas. IceBank has been installed in over 4,000 installations including hospitals, malls, colleges and offices. If you are looking at replacing part or your entire existing HVAC infrastructure, it’s worth taking a look at CALMAC. For new construction, payback can be immediate. During a chiller replacement, Icebank retrofits are on par or lower with other types of HVAC projects with a typical 3 to 5 year payback period. The difference is the extended lower energy costs for the life of the system and the flexibility to disconnect cooling requirements from energy purchase times.
CALMAC can provide both full- and partial- load thermal energy storage systems. The essent... Learn More