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+---
+tags: HVAC, hydronics, chiller
+---
+
+# Heat Recovery Chiller
+
+This is an article that I wrote back in 2020, but I don't believe that I published it anywhere, so
+I'm doing it now. I did discuss this on
+[this episode of the HVAC School Podcast.](https://hvacrschool.com/podcasts/is-the-future-of-air-conditioning-self-contained-propane-chillers/)
+
+## Heat Recovery Chillers
+
+I have always had a love and passion for hydronic systems, perhaps it's because they are not that
+common in most areas. The designs tend to be elegant and the flexibility is unparalleled by most
+equipment choices currently available in the U.S. I'm going to try to not get too far into the weeds
+in this article, but offer an overview of what I feel would be my dream system.
+
+## The Source
+
+A heat recovery chiller will do simultaneous heating and cooling, as opposed to a traditional
+heat-pump or reverse cycle chiller that can only operate in one mode at a time. This system would
+have a second refrigerant to water heat exchanger and utilize the air-source when we don't need to
+bank / store heat, or are running in heat only mode. There are several benefits to this style
+system, the main being that while operating simultaneous heating / cooling mode the COP of the
+system doubles. For example, the [Multi-Aqua MHRC2](https://multiaqua.com/mhrc2/) shows a COP of
+about 8, which is approximately equivalent to 30 EER or 34 SEER. This gives us geothermal level
+performance without the need of a field.
+
+## Indoor Portion
+
+The indoor portion of the system, we would utilize buffer tanks as thermal storage for the chiller.
+The buffer tanks give us several benefits, including longer run times for the chiller, load
+matching, and the ability to size for larger load (heating or cooling) without some of the problems
+that occur when over-sizing a traditional system. The buffer tanks also allow sizing more
+aggressively by having storage during peak load conditions.
+
+![buffer](/articles/images/2023-10-27-buffers2.png)
+
+This shows a cooling buffer tank as well as a heating buffer tank. The horizontal pumps are what
+circulate water through the chiller, while the vertical pumps are what distribute the water to the
+load / emitters. This configuration allows for water to be used for the loads first and extra
+capacity to go into the buffer tanks. The buffer tanks also offer hydraulic separation for the pumps
+(meaning that they won't interfere with each other if / when there are different flow rates).
+Another advantage of the buffer tanks is that you can connect multiple heating or cooling sources in
+parallel to the system. This is shown by the extra tees in the hot buffer tank where we could
+connect something such as solar water collectors, pellet or wood boiler, or a conventional boiler.
+You'll also notice on the right side of the hot buffer tank, that I am showing a brazed plate heat
+exchanger that would be used to supply domestic hot water.
+
+## Distribution System
+
+This could be a number of things, from radiant panels, in-floor, high-output baseboard radiators,
+however I'm going to model it as a 4-pipe hydronic air handler.
+
+![ah](/articles/images/2023-10-27-ah.png)
+
+The hydronic air handler is able to provide cooling, heating, and re-heat dehumidification, all in
+one package. With a hydronic system, it would be very easy to load match by controlling the fan
+speed and utilizing a Delta-T pump or outdoor reset controls. These air handlers are available from
+several manufacturers and come in different styles from traditional (as shown), small duct high
+velocity systems, and even ductless styles.
+
+## Disadvantages
+
+1. Not highly available in the U.S.
+1. When the chiller is down nothing works (not much different than traditional)
+1. Lack of understanding / technicians afraid to work on this style system.
+1. Potentially higher upfront costs.
+1. Lack of design or planning could cause unhappy clients (same with traditional)
+1. Distribution systems need to be designed around low water temperatures (not a drop in replacement
+   for traditional boiler systems)
+
+## Advantages
+
+1. Central plant for heating, cooling, and DHW (also a disadvantage)
+1. Flexible distribution options / methods.
+1. Self contained refrigerant circuit
+1. Ability to produce / store thermal energy during off peak electrical hours
+1. Ability to move BTU's more efficiently through water than air
+1. Long life for distribution system (50-100+ years)
+1. Easier transition to natural / flammable refrigerants
+
+## Conclusion
+
+In conclusion, there are many advantages to this style system, as well as disadvantages. One of the
+main points is to think of the system in 3 distinct components, the source(s), thermal storage, and
+distribution. As mentioned, this only one concept, but in reality, there are many ways to accomplish
+this, which is one of it's advantages. For example, perhaps in certain scenarios it makes sense to
+dump excess heat into a pool, create ice storage during off peak hours, cascade into another water
+-> water heat pump for higher temperature distribution, incorporate solar collectors, and so on.
+
+Thank you for reading all the way to the end!