The Challenge of Retrofits

As a result, building owners must retrofit their buildings to reduce on-site fossil fuel use. These policies are pushing commercial building owners toward heat pump technologies. Using electricity as a power source, heat pumps can provide both heating and cooling functions without emissions from fossil fuels. In residential settings, air-to-air heat pumps are the most common type of heat pumps used, due to their ability to heat and cool with a single piece of equipment.

With the widespread adoption of electric heating in commercial buildings, hotels, hospitals and industry, air-to-water and water-to-water heat pumps are gaining momentum globally as a long-term integrated approach with a lot of potential due to their increased efficiency and ability to operate at lower ambient temperatures. Water-to-water heat pumps, which absorb heat in the evaporator in a waterside or hydronic system and then reject the heat through the condenser on the other side, can provide a sustainable heating source by allowing the building to recover rejected heat and reuse it, thereby saving energy and heating costs, while also reducing carbon emissions.

But in commercial buildings that currently use a combination of chillers and boilers, retrofitting with an air-to-air or air-to-water heat pump is a challenge. In cold weather, it’s very difficult to use the ambient air as a heat source and still heat water above 40 degrees Celsius. A hydronic heating system utilizing a heat pump generally requires at least 45-degree Celsius water to effectively heat. Air-to-water heat pumps are also currently at least 10-15% less efficient than water source heat pumps due to low ambient air temperatures and air-to-refrigerant heat transfer approach.

Alternative Solutions

Utilizing other heat sources is possible and, in terms of efficiency, makes a lot of sense. Heat recovery is gaining momentum globally as a way to provide heat in a more efficient and sustainable way. For example, using waste heat from data centers, commercial refrigeration systems, or wastewater treatment plants provides a steady and predictable source of heat all year round. In addition, these heat sources could be centralized near the heat source, creating the opportunity for district heating and cooling. Entire blocks of buildings could share resources to build an incredibly efficient district energy system and contribute heating or cooling to each other in an integrated symbiosis system. This is happening in many European cities and on some U.S. college campuses. Unfortunately, in most areas of the U.S., not only do we not have the district energy infrastructure to share heating and cooling between buildings, but we lack the business models and regulatory structures as well.

Rather than try to crack that regulatory nut, the industry is moving toward air-to-water heat pumps instead of a chiller and boiler combination. The climate, however, cannot wait until the next generation of air-to-water heat pumps are available for us start decarbonizing our commercial buildings. Hybrid solutions that can significantly reduce both emissions and operating costs can be implemented today. Combining air-source heat pumps with natural gas-fired heating does not eliminate fossil fuels altogether, but it can reduce the need for fossil fuels to the very coldest days of the year. In certain areas of the country — the mid-Atlantic, Southeast or South — that may only be a few weeks a year, depending on winter temperatures, building envelope and heating system design.

Dual fuel systems, which use heat recovery chillers in combination with a boiler, are also an innovative approach to reducing carbon emissions in cases where building owners aren’t ready to replace their functioning boiler. The system can use the existing boiler with a flue gas scrubber, which provides cooling and removes contaminants from the atmosphere, to recover heat through a water-to-water heat pump, pre-heating the boiler feedwater and partially electrifying the heating system.

Danfoss continues to advocate a comprehensive approach to decarbonization. Utilizing heat pump technologies in new building design and retrofits will go a long way toward reducing carbon emissions and achieving compliance with local, state, and federal regulations. In addition to reducing emissions, using electricity as a power source creates more energy-efficient heating systems, often resulting in significant savings for building owners and increased comfort for occupants. Using oil-free compressors and variable-speed technology, Danfoss is developing components for the next generation of heat pumps, which will be more efficient and higher-performing as commercial buildings move toward full electrification.