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