Buildings Magazine - Buildings 1/2015

Match VRF to your building’s loads, location and lifecycle costs
VARIABLES FOR
RETROFITTING
with VRF
ENERGYMANAGEMENT
Variables create anxiety. We want to remove as many variables as possible from a situation. However, you
can embrace the variables in variable
refrigerant flow (VRF) systems
because they are a major contributor
to their efficiency. But you will need
to address some variables about your
building in order to determine if VRF
technology is a good retrofit option.

A VRF system’s variable flow of refrigerant via variable frequency drive (VFD) motors allows the system to adjust to a variety of loads. The refrigerant serves as both the heating and cooling medium that can be delivered to multiple fan-coil units from a single outdoor condensing unit.

A VRF system with heat recovery allows indoor units to cool or heat as necessary. For example, instead of rejecting heat from a server room to the outside, a VRF system can move the heat to perimeter spaces that require it.

For retrofit applications, VRF can offer a solution for inefficient fans and leaky ductwork. Buildings with inadequate cooling may be a particularly good fit. Older facilities and historical buildings, which often cannot easily accommodate new HVAC equipment, may also be targets for VRF solutions.

If you’re considering a major retrofit of an existing HVAC system, take these three steps to do your due diligence for a possible VRF solution, says Anne Wagner, energy efficiency engineer at the Pacific Northwest National Laboratory (PNNL).

1) Screen by building characteristics – Some older buildings may provide better paybacks for VRF than new ones, according to Variable Refrigerant Flow Systems, a technology assessment prepared under GSA’s Green Proving Ground program ( www.gsa.gov/greenproving- ground). Wagner, who is a co-author of the publication, points out that buildings with high energy usage, particularly those with VAV systems with electric reheat or other electric resistance heat, may be good candidates. Facilities with limited space to add ductwork for additional cooling capacity may also be good candidates. The comparatively small size of VRF refrigerant lines makes them easier to install than ductwork even when buildings have adequate space.

The GSA report notes a number of factors to consider when evaluating a cost-effective match with VRF technology. The zonal capability of VRF fan units are well-suited to facilities with separated spaces, including schools, lodging, multifamily, healthcare, some shopping centers, and office buildings with numerous enclosed spaces and conference rooms. Conversely, big box retail, warehouses, and other facilities with large open spaces are not typically suitable.

Climate is also a factor, with extreme weather being a plus. Colder regions may offer better opportunities for heat recovery and may increase savings if converting from any type of electric resistance heating. Conversely, buildings in mild climates that often operate in an economizer mode will benefit less. According to the report, a sweet spot for VRF in terms of building size is 10,000–100,000 square feet.

2) Do an energy analysis – Have your building surveyed to understand how, where, and when it uses energy – and wastes it. Energy engineers recommend incorporating a minimum of one year’s worth of detailed consumption data in order to model the building through the seasons. The analysis will provide a platform for determining proper size as well as estimating the efficiency and cost of new systems.