By Drew Turner
Electric heat pumps become a more viable option for commercial sites Identifying alternative energy sources has become a key objective for many organizations as they strive to decrease energy costs and reduce their carbon footprint.
For most organizations, the production of heat is the largest individual application of energy, and space heating for buildings is one of the largest components of that output. Efforts to reduce the carbon emissions associated with building heating has led organizations to consider replacing traditional HVAC equipment with electric-driven options, such as heat pumps. For many, this is the next step in the decarbonization of heating. The electrification of building heating can provide significant benefits, allowing operators to not only reduce carbon emissions, but also remove NOx (nitrogen dioxide) and SOx (sulfur dioxide) emissions, improve energy efficiency, and reduce operating costs. This change also provides a building’s power providers with the opportunity and flexibility to meet increasing demand with carbon free, renewable sources.
A challenge for considering electric heat pump technology in commercial applications is a longer ROI payback period than many organizations require to justify investment. Further, moving to heat pump technologies has previously required the changing out of demand-side equipment, to enable operation at significantly lower heating temperatures. Luckily, research into heat pump equipment using oil-free, magnetic bearing, centrifugal compressors indicates that this technology may bring the payback periods into a more palatable range for commercial clients.
Expanding options for heating
There are several types of compressors commonly used in HVAC applications, which fit in the two categories of either positive displacement or dynamic (centrifugal or axial) technology.
In positive displacement versions, such as screw compressors, energy is used to generate pressure, and the refrigerant is squeezed to add energy to it. In the centrifugal/dynamic versions, refrigerant is thrown, increasing kinetic energy.
It is possible to move a high volume of low-pressure refrigerants rather efficiently in a centrifugal/ dynamic compressor, due in part to kinetic forces. Unfortunately, due to the need to generate a higher differential (“lift”) temperature in heating applications, these compressors, while common in cooling applications, have heretofore mainly been precluded from heating applications.
With the use of magnetic-bearing technology, it is now possible to press these compressors into service for heating applications as well.
Heat pump designs mainly follow one of three setups: air-to-air, air-to-water, and water-to-water. Air-to-air heat pumps extract heat from ambient air. While heat pumps present an efficient HVAC option, these units tend to have lower efficiencies than other heat pump setups, since they extract heat from what can be very low temperature ambient air. They generally offer the lowest capacity of the available setups as well. While common in residential applications, they are not likely to be adapted to the higher demands of commercial or industrial applications.
Perhaps the fastest and easiest way for a building to begin to benefit from heat pump technology is to replace existing HVAC heat-source equipment with an electric air-to-water heat pump, with oil-free, magnetic bearing, centrifugal compressor technology. This type of retrofit can typically be done quickly, with minimal disruption, within the existing footprint onsite.
This type of heat pump can be quickly implemented and yield increased energy efficiency. When considering air-to-water heat pumps, it’s important to note that while these new compressors have greater operating temperature flexibility than their predecessors, they still have limited operating temperature flexibility, due to the lower efficiency of air-to-water heat transfer, as well as the high variability of climate driven air temperature. This means an oil-free, magnetic bearing, compressor-based air-to-water heat pump would be able to provide sufficient heat in mild-to- temperate climates, but likely not at the coldest ambient temperatures found in harsher climates.
A water-to-water electric heat pump, driven by oil-free, magnetic bearing, centrifugal compressor technology, would not have issues stemming from operating temperature limitations at the lowest ambient conditions.
The efficiency benefits accrue because the heating process begins with water, rather than with air. Water can be a much warmer medium to start with; it transfers heat more efficiently than air, and thus demands less energy to boost the heat to the target temperature. River water, for example, can be dozens of degrees warmer than the surrounding air, even on a cold winter day.
The setup logistics of a water-to-water electric heat pump can be more ambitious, and require a larger upfront investment. For example, a source of water must be nearby, and piping infrastructure would need to be built to access it. But innovative users often find ways to get faster results. For example, it is also possible to operate these heat pumps with nearby groundwater/ground energy using a geothermal loop. And some use the water-to-water concept to compound the benefits by reclaiming heat from an industrial process or other source which is otherwise rejected to ambient, if such is available.
With the development of magnetic bearing, centrifugal compressor technology, heat pump designers have a new tool to help customers achieve their goals of lowering operating costs and carbon emissions.
Working from a centralized plant
Not a system architecture that is widely used in Canada, but possibly offering some of the greatest benefits, would be the use of a series of electric heat pumps using magnetic bearing centrifugal compressors, and operating them from a central location. The heat could be piped to a series of buildings in a “district heating” model.
While district heating is used in some North American cities, it is more common on university, hospital and corporate campuses where related buildings are in close proximity. And it is far more common in Europe, being used in municipal grids of all kinds. This may require significant new infrastructure and licensure, but the payback period can be surprisingly compact. Where existing district heating infrastructure exists, it may be possible to swap in heat pump technology and make use of the piping and other components.