TECHNOLOGY
Heat Pump
A heat pump is a machine that transports thermal energy from a cold to a warm environment. Heat pumps garner much praise for their energy efficiency because rather than generating heat, these machines simply transport heat from one environment to another. While heat is only able to diffuse from hot to cold, this device is able to move against the natural temperature gradient through the use of electricity and most importantly, a refrigerant fluid with a low boiling point.
This refrigerant fluid circulates through a warm and cold reservoir through a network of pipes, continuously absorbing heat from the cold reservoir and releasing the heat into the warm reservoir. A heat pump system consists of a compressor, condenser, expansion valve, and evaporator. From the lower temperature side, the fluid moves through the evaporator coils where a fan directs warmer outside air on to the coils. This allows for the liquid refrigerant to absorb heat and transition into a gaseous state. The pressure and subsequently, the temperature of the gas, is further increased as the vapor passes through the compressor. From the compressor, the gas passes through the warm reservoir where it releases heat as it cools through the condenser coils. Now back in it’s liquid form, the refrigerant passes through the expansion valve into the cold reservoir and the process begins again.
Figure 1 : Heat Pump Cycle
The efficiency of a heat pump is measured upon the coefficient of performance (COP). The COP is measured by the temperature of the heat being transferred over the whole temperature difference.
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Therefore in order to achieve maximum efficiency, the temperature difference through which the heat is displaced should be at minimized. A higher COP corresponds to a greater system efficiency with COPs typically ranging from 3.0 - 7.0 (300% to 700%) [1] . For this reason, heat pumps work best in moderate climates. Data from the National Oceanic and Atmospheric Administration suggest that San Luis Obispo County has a fairly mild climate with a consistent winter low around 45-50 degrees and a summer high of 70-80 degrees fahrenheit.
Variable Flow Pump
A variable flow pump, is as the name implies, a pump that can rotate at a chosen speed, opposed to normal pumps which operate at either a single speed or a few predetermined speeds. Having the ability to choose the speed at which the pump is run allows for less power to be drawn overall because it is not necessary to always have a pump running at full power. Another advantage of variable flow pumps over just a multi speed pump its that they have pressure sensors and automatically adjust the flow rate to provide for the most efficient speed for filtering, heating, and cleaning.
The reason replacing the pump is important is that pumping system consumes 70% of the total energy going to the pool. Variable flow pumps are stated to save anywhere from 70-90% on energy costs compared to single speed pumps. These numbers come from the Pump Affinity Law which states that “ the change in power drawn is proportional to the cube of the change in speed, where change in flow is proportional to the change in speed, and change in head is proportional to the square of the change in speed”2. So the variable flow pump is able to reduce the power consumption by reducing the motor’s speed, when it senses it can, which creates less resistance within the pool system. Since the relationship is cubic the change in flow rate exponentially decreases the amount of power required. Some numbers can be seen in the figure below from a paper published by the Consortium for Energy Efficiency.
Figure 2: Some energy savings estimates
These numbers are assuming that 3450 RPM is the speed that most one speed pumps run at, and that running it at half power requires to be run extra time. They go on to note that these numbers are what is expected, however the actual systems will not have this much energy savings, but that even so the energy savings is substantial.
1. https://www.poolcenter.com/variable-speed-pumps
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2.Eaton, Eileen. “CEESM High Efficiency Residential Swimming Pool Initiative.” Energy Efficiency Library, Consortium for Energy Efficiency, Jan. 2013, library.cee1.org/system/files/library/9986/CEE_Res_SwimmingPoolInitiative_01Jan2013_Corrected.pdf.
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Figure 1 - https://www.sciencelearn.org.nz/images/232-basic-heat-pump-cycle`