Water vs. Air: Variable Speed Technology

Water vs. Air: Variable Speed Technology

Posted by Greg Cunniff, Applications Engineering Manager, Taco, Inc.

Variable speed hydronic circulation has been around for years, and with the advent of packaged controls on pumps, it’s easier than ever to implement.  Variable speed pumping operates on this simple principle: it is based on heating or cooling load demand.

The objective is to satisfy the heat gain of a structure as efficiently as possible. The way to do that is to allow a pump to adjust its speed to deliver the required heat. By maintaining a consistent delta-T, flow can be varied as needed to ensure optimal performance and heat transfer.

Chilled water systems have employed variable speed fans with variable air volume (VAV) systems for more than a quarter of a century as well as variable speed pumps.  DX-type systems have essentially functioned as constant volume systems using one evaporator coupled up with an air-cooled condenser along with a set of refrigerant pipes in between.

DX manufacturers have finally incorporated variable speed technology within their systems, using multiple evaporators on a single condensing unit, essentially making a chilled water refrigerant system. To make the system work, a variable volume of refrigerant is needed for each evaporator. So the good news for DX systems is that their level of efficiency has increased, just as it has increased for all-air systems, VAV and variable volume chilled water systems.

With today’s refrigerants, like R410, compliant with the Montreal Protocol’s direction for less environmental impact, they are not as efficient as previous CFC refrigerants in generating the amount of BTUs needed for today’s systems. Today with rising energy costs and the use of less efficient refrigerants there’s a need for variable speed technology to provide higher efficiencies.

What’s your opinion of variable speed technology and its energy efficiency impact? Are you employing VFD-equipped pumps and compressors?

Next up: The safety issue with VRV/VRF systems.


2 Responses

  1. Variable makes sense, and as complex as DX variable is, variable water is easy. R-718 – water – variable without danger (no low pressure switches). Williams variable fan coil – leaving air temperature control is demand controlled energy efficiency – with valves or circulators – why go “ON-OFF” when variable makes sense?

  2. It’s amazing to pay a quick visit this site and reading the views of all colleagues about this paragraph, while I am also eager of getting know-how.

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