By ROBBIE SVIDRON, Engineering Education Manager, Intellihot Inc.
Heat pump water heaters have cemented their position as the most viable future-proof technology for decarbonizing water heating systems. With several states banning the use of natural gas in commercial buildings, businesses like restaurants, hotels, and multifamily properties have continued to assess heat pump water heaters for their facilities. Apart from favoring sustainability, the technology promises exceptional efficiency, providing the opportunity to realize significant OpEx savings as a result.
However, the implementation of heat pump water heating technology appears riddled with challenges. Addressing these challenges holds the key to unlocking the full potential of heat pump water heaters.
Challenges With Heat Pump Water Heaters
Engineers have found it difficult to assess the true on-field performance of existing heat pump water heaters. Constantly-changing environmental factors like ambient temperature and hot water loads directly impact the performance of heat pump water heaters. Hence, commercial properties find it difficult to assess how much heat pump water heating equipment they need to reliably meet their hot water demand. Plus, while heat pumps are very efficient at moving heat, they do so at a much slower rate than a conventional gas-fired boiler.
Uncertainty in performance leads to a cost barrier for commercial properties. Being unsure of the right amount of heat pump water heating equipment needed could lead to businesses erring on the side of oversizing. Assuming the need for more heat pump water heating equipment drives up the upfront cost. The fact that heat pumps move heat slower than conventional gas-fired boilers increases this tendency to oversize.
Additionally, heat pump water heaters demand a thorough audit of building infrastructure to ensure that there is sufficient electrical infrastructure, space, and ability to meet hot water loads in cold weather. These considerations, in turn, lead to larger upfront costs for the end-user as equipment costs can double or triple that of a conventional boiler system.
Cost is not the only downside to oversizing due to performance uncertainties. More heat pump water heating equipment results in significantly higher space consumption. This scenario is especially true when businesses try to counter performance uncertainties by increasing potable hot water storage to have peace of mind. Higher space consumption is a huge barrier for heat pump implementation, especially for facilities like restaurants.
Fortunately, there are three factors that can help alleviate these challenges and speed up heat pump water heater implementation: an on-demand design, advanced sizing methodologies, and in some cases, hybrid systems.
Tankless Heat Pump Water Heating
Tankless heat pump water heaters can be a game-changer when it comes to HPWH implementation. How does tankless technology work in a heat pump water heater? Currently, tankless heat pump water heaters employ a thermal battery to store the heat captured from ambient air. Use of thermal batteries cut space needs by 40% over traditional heat pump technology, while doubling available hot water, allowing these heat pumps to fit in existing mechanical rooms. Potable water is pulled through a heat exchanger suspended in the thermal battery discharging the stored energy on demand.
This thermal battery design allows the heat pump water heater to decouple energy storage from the potable water used at the fixtures, thus acting like a traditional tankless water heater. The thermal battery can be integrated with the heat pump unit in a combined design, or housed in a separate unit. Tankless heat pump water heating results in various benefits that can alleviate the aforementioned challenges.
- A tankless approach offers design simplicity. Without the need to rely on storage tanks or mixing valves, on-demand heat pump water heating makes implementation much less complex;
- The lack of such external components negates the need for complex controls;
- With fewer components prone to failure, this approach increases reliability too;
- A tankless approach saves a large amount of space by eliminating bulky storage tanks;
- With no potable water storage, an on-demand heat pump water heater also mitigates the risk of Legionella.
Advanced Heat Pump Sizing Methodologies
Next, advanced sizing methodologies can help counter the performance uncertainties of heat pumps. Some manufacturers have developed simulation-based, multi-dimensional sizing tools that can incorporate advanced modeling techniques to consider dynamic factors like ambient temperature.
A reliable sizing tool will take several factors into consideration. It should be able to incorporate geographic parameters like seasonal and hourly temperature changes. A reliable sizing tool would also be able to predict hot water demand for each commercial property type based on flow rate data from other properties of a similar type in a similar geographic location. Identifying tools that guarantee their sizing results can help ease the uncertainty of choosing the right amount of heat pump water heating equipment.
With accurate sizing, properties can avoid oversizing while being able to meet their hot water demand reliably. This can help properties reduce upfront cost as well as space and electric power needs, essentially making the barrier to implementation smaller.
Hybrid DHW Systems
Finally, challenges with heat pump water heating have sparked interest in hybrid DHW systems that combine the fast delivery rate of high-efficiency gas with the sustainability and performance of heat pumps. In regions where natural gas is still permitted, pairing a heat pump water heater with a gas-fired water heater can help alleviate high upfront costs. Hybrid systems can open the door to electrification, allowing commercial properties to progress towards complete decarbonization in small, feasible steps.
These “hybrid” water heating systems mirror their counterparts in the automotive industry, where electricity is used where possible, with the ability to rely on gas power as a backup when conditions call for it. Commercial on-demand systems work best for such hybrid systems: mitigating Legionella growth, while also reducing standby losses and purging losses in the case of gas-fired equipment. These hybrid systems can be configured in many ways. Here are three examples:
- Heat pump water heater for primary load, gas water heater for recirculation;
- Heat pump and gas units staged in parallel;
- Heat pump water heater receives incoming water first with a series connection to the gas-fired unit acting as a booster.
Approach #3 can be considered the best option from the above as it maximizes heat pump usage: keeping operational expenses low, while helping cut down upfront costs.
When compared with a heat pump-only system, hybrid systems can significantly reduce the difference in upfront cost. In return, the hybrid system has the potential to substantially reduce operating costs and electrical consumption, boasting a quick payback to recoup costs. Utilizing an advanced sizing tool with the ability to run multiple simulations (described previously in this article) can help engineers design a hybrid system reliably.
In conclusion, heat pump water heating technology brings in a fresh set of opportunities and challenges. While heat pumps promise decarbonization and energy efficiency, their implementation can be marred by performance uncertainties, high upfront costs, and high space needs. However, unique solutions like a tankless design, advanced sizing methodologies, and hybrid systems can help alleviate these challenges. By doing so, they can open the door towards complete electrification slowly, allowing commercial properties to aim for zero reliance on natural gas in small, manageable steps.
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Based in the Chicago area, the author holds a mechanical engineering degree from Bradley University, and currently serves as Intellihot’s sales engineering and education manager. Formerly a mechanical systems and applications engineer, Svidron has extensive field knowledge and expertise in multiple water heating systems for a variety of different geographies.