HVAC School - For Techs, By Techs
Q&A - Sizing Heat Pumps for Heat Load - Short #213
· Summarized
Key takeaways
- In most scenarios, heat pump heating loads will be greater than cooling loads.
- Oversizing heat pumps can lead to issues like short cycling, inefficient energy use, and inadequate humidity control.
- Variable capacity systems can mitigate problems associated with oversizing and improve overall HVAC performance.
- Future technologies such as heat recovery systems promise to optimize the balance between heating and cooling loads.
Summary
Understanding Heat Pump Sizing
In this episode, Bryan addresses a listener question regarding the sizing of heat pumps and explores the implications of oversizing heat pumps for heating loads compared to cooling loads. He notes that generally, heating loads exceed cooling loads, and emphasizes the importance of accurate sizing to maintain efficiency and comfort in HVAC systems.
The Risks of Oversizing Heat Pumps
Bryan discusses the common concerns surrounding the oversizing of heat pumps, particularly in humid climates where short cycling can lead to energy inefficiency and discomfort due to inadequate humidity control. He suggests that while it is generally inadvisable to oversize for cooling, encountering scenarios where cooling loads exceed heating loads is not necessarily problematic.
Variable Capacity Systems as a Solution
Bryan emphasizes the value of variable capacity systems in addressing mismatches between heating and cooling loads. These systems provide flexibility for different load conditions, potentially minimizing issues caused by oversizing while optimizing efficiency.
Future Developments in HVAC Technology
Looking ahead, Bryan expresses excitement about innovations that will allow for better matching of heating and cooling capacities, such as heat recovery systems with buffer tanks. This could lead to enhanced performance and comfort in HVAC applications.
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Show notes
In this short Q&A podcast, Bryan answers a listener-submitted question about sizing heat pumps for heat load in heating mode, something that we haven't talked much about in the past due to the greater need for cooling in our market.
In most cases across the country, a heat pump's heating loads will be greater than the cooling loads. There is a greater swing between the desired temperature and the actual temperature in heating mode than in cooling mode (in terms of sensible BTUs). We don't want to oversize for cooling because of its lower efficiency, comfort, and humidity control due to the shorter runtimes. (However, oversizing for cooling loads is far less of an issue in arid climates.)
We don't want to oversize the heat pump to meet the heating load when we'll far exceed the cooling load. However, that's not much of a concern for the opposite scenario in which we oversize for heating to meet the cooling load. We can add auxiliary heat, such as electrical heat or natural gas in dual fuel setups, to help us meet the heating load; we don't have those same options in cooling. Variable-capacity systems can also be beneficial in scenarios where heating and cooling loads are massively different.
Bryan is excited about future opportunities for standby cooling and heating capacity, such as in the case of a heat pump heat recovery chiller system with buffer tanks. In the meantime, we have to design for vastly different heating and cooling loads and may have to oversize for one or the other.
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