New Air-to-Water Heat Pumps Arriving in America

By Hoyt Corbett

For the first time hydronic contactors are being offered factory packaged, integrated heating and cooling devices that have high efficiencies and great appeal in the green building market. An exciting new generation of air to water heat pumps based on variable speed inverter technology offer hydronics a huge new opportunity. Previously, radiant floor heating and other forms of hydronic heating have required the additional expense and complexity of another distinct HVAC system to do cooling. Now it will only require adding air handlers with condensate drains, changeover valves and some insulated piping.
While air-to-air heat pumps have been well established in North America, the Hydronic industry has needed highly efficient and packaged air-to-water heat pumps to make its next growth surge. Previous air-to-water reverse cycle chillers and heat pumps did not feature variable speeds, were not packaged as well integrated units for heating, cooling and domestic hot water with solar thermal options. These models were less efficient and often noisy. That is now changing with the introduction into North America of a sophisticated new generation of air-to-water heat pumps based on variable speed inverter technology. The already introduced Daikin Altherma, as well as introductions by Mitsubishi, Toshiba, Aermec and others, will offer HVAC and hydronic contractors great new possibilities for heating cooling and inter-ties with solar thermal. This spells tremendous opportunity in both commercial and residential applications for hydronic contractors if they take advantage of it.

Using sophisticated controls with inverter technology to run a variable speed compressor reduces cycle losses, and a big turn down ratio adds comfort by load matching, saves electricity and extends the life of the compressor. Most of these units will come packaged to do both heating and cooling, use a strategy to make or at least to preheat domestic water, and tie in to solar thermal systems. Heated water is made by means of a refrigerant-to-water heat exchanger.

Run in reverse, cooling may be taken off the refrigerant side with a dx coil, or chilled water may be generated with the refrigerant-to-water heat exchanger. Different manufacturers are making different choices in their initial offering in terms of which way to do cooling. For the residential market most companies are offering cooling with chilled water. For hydronic contractors, cooling with chilled water opens up a huge new aspect of the trade, and one that uses familiar piping and pumping methods. These units can offer high coefficients of performance (COP) that, particularly in milder climates, can compete well with geothermal heat pumps and offer much simpler, less environmentally intrusive and less costly installations. Manufacturers claim (heating) COPs in the range of 3.0 to as high as 5 in milder climates. At these efficiencies, these units offer a significantly lower carbon footprint than fossil fuel choices, even after allowing for all the distribution losses and fossil fuel contribution for the North American electric grid. This fits in very well with green building. Since the units reduce the overall energy consumption of a project, it becomes more cost feasible to offset the overall energy use of a project with PV. David Knight of the Monterey Energy Group in Monterey, California has now specified close to 100 Daikin Altherma’s — all with solar inter-tie, and most also with PV — to get to net zero. David noted that “combining these multi purpose heat pumps with PV is particularly attractive to green conscious clients and a good fit in states like Oregon, California and others that have good PV rebates. It insulates them from future rises in energy costs. And economically, it is particularly attractive in areas with low electric rates or areas without natural gas.

To take advantage of this new opportunity, contractors will need to master and correctly apply the design constraints of the units. On the heating side these heat pumps produce modest water temperatures (120°F-130°F). With radiant floor heating this requires the use of high output radiant floor assemblies, and will place limitations on the R-Value of floor coverings and require careful design. And while forced air fan coils may be used, they must be ones with extra rows of coils specifically designed for lower water temperatures. Cooling with chilled water will mean that hydronic contractors will have to learn about selecting fan convectors with condensate drains and must insulate pipes against condensation. As the outdoor temperature decreases, the output of the unit also decreases, so the units must be sized at the design temperature. However, since the variable speed inverter technology has such high turn down ratios (as high as 30-1) this is not much of a problem. Another design issue is that the units may efficiently make domestic hot water, but will only recover according to the sizing of the unit. Today’s small, tighter, more efficient homes often mean these units can be small in output for heating and cooling. Most Americans demand more hot water than their European or Asian counterparts. Many American contractors are realizing this means installing bigger domestic water tanks than has been normal in Europe or Asia. To optimize the efficiencies and for lowest operating costs, contractors and operators will have to become knowledgeable about how to schedule and control these sophisticated units so that the use of back up heat is kept to a minimum. Selecting the best air-to-water heat pumps with regard to domestic hot water production may require some careful probing, since the units will likely be rated in heating and cooling, not for their domestic hot water capability. Units that are not integrated in the production of heating and domestic hot water are likely to be compromising domestic hot water production, efficiency or both.

These air-to-water heat pumps are crossover products. There is considerable debate over who should distribute, support, sell and install these products. The heat pump end is more traditionally an HVAC product with refrigerant, and the other end is a hydronic product that requires knowledge of hydronic design and installation. The specialty hydronic contractors have a much bigger incentive to develop the market for these products than their air side competitors since unlike many HVAC contractors they are not already selling air to air to air heat pumps. The next few years will determine if smart hydronic contractors aggressively move into this business or if it languishes with more traditional air side businesses. To be successful hydronic contractors will need to learn about cooling with chilled water and about the refrigeration technology in the heat pumps.

These air-to-water heat pumps are too new to the North American market to have garnered the political support that would qualify them for federal tax credits. The best test data on these units is from Europe and Asia; there is no current standard in the US for testing inverter technology air-to-water heat pumps. One choice is to test them according to air-to-air procedures, but these do not reflect the efficiencies of air-to-water and variable speed inverter technology. These tests call only for a low and a high-speed test, and do not account for the fact that with variable speed technology a unit will almost always be running in between. While these issues may somewhat slow down adoption, the benefits of these new units are so obvious that they are already gaining market acceptance. Already, electric utilities are testing them for inclusion in rebate programs. The combination of efficiency, a low carbon footprint, the ability to provide heating, cooling and domestic hot water with a solar thermal option means these new air- to-water heat pumps should generate a big growth in hydronics.

Hoyt Corbett is a patented inventor and develops products for Precision Hydronic Products. His products may be found at www.hydronic workshop.com and also at www.ecowarm.us. He may be reached at via email at inventivedevelopment@yahoo.com.