by Jared Carpenter
Sanborn Place and Sanborn Home Care is a not-for-profit corporation providing living and health assistance to 73 residences. In 2012, Jacqueline Carson, the director of Sanborn Place, embarked on a plan to upgrade the facility, including the facilities’ HVAC systems, with a final goal of providing greater comfort to the tenants and reducing overall energy consumption. Upon completion, RDK Engineers was asked to measure and verify the electricity, demand, and gas savings to ensure the return on investment numbers were being met.
Sanborn residences each have a heating and cooling system in the bedroom and living room. The existing system consisted of hot-water baseboard heat and wall-sleeve air conditioning units. This common system provided insufficient cooling and variant heat because of the age and lack of unit control. However, installing a central chilled water system or packaged rooftop unit was impractical due to construction limitations and the fact that installation would be too intrusive to the residents who would remain in their units through the duration of the construction.
Rather than retrofit the existing system with a similar design, Carson and the board of directors opted to install a variable refrigerant volume (VRV) system with the intent of saving energy and increasing comfort. The VRV system uses an inverter-driven compressor which is capable of efficiently providing simultaneous heating and cooling. The system consists of over 150 wall units, which provide isolated heating and cooling, but only 16 rooftop compressor-driven units. This design allows energy to be shared between multiple units prior to using high energy use compressors to meet the thermal needs. For example, the east side of a building and the west side of a building have very different needs due to solar loads. The VRV system will balance the thermal energy and only use the compressor if further cooling or heating is needed. When additional heating or cooling is called for, the compressor will engage until space conditions are met. This allows tenants to have a system that is quieter, zoned with more accuracy, minimizes maintenance as no system is strained due to overuse, and reduces energy consumption.
Increased comfort due to the accuracy of the systems and the low noise level proved to be a secondary benefit when compared to the energy savings. In order to estimate the savings, the year 2011 was used as a baseline. The energy savings was over 97,000 kWh which totals a 23% decrease. The demand reduction was also a major component of the savings. The VRV system creates more stabilized consumption. This results in a peak demand reduction of almost 50 kW. In addition, the gas usage was reduced by over 40% annually.
RDK’s Energy Group verified the energy savings by reviewing the utility bills, placing data loggers, and measuring demand (kW) during variable operating times. The end result is a cost savings of $27,326 annually. This, along with the rebate from the utility, results in a simple payback of 1.1 years. In addition, the new systems with linked HVAC systems allow easy monitoring of the units for comfort and energy savings. This central automation monitoring system allows the Sanborn Place staff to ensure optimum comfort for its residents while achieving an energy use index (EUI) score of just over 50.
Jared Carpenter is senior energy engineer at RDK Engineers.