One or more embodiments of the invention generally relate to pumps. More particularly, certain embodiments of the invention relate to liquid or gas moving systems with variable diameter impeller.
The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.
It is believed that electrical power costs for centrifugal water or air pumps may account for a large portion of the operating costs for the most common mechanical equipment used throughout the world's buildings. Centrifugal pumps are common equipment in many industries because they are typically simple, effective, and inexpensive. Impellers are the rotating part of a centrifugal pump to move a fluid by rotation. The rotating part may also be turned by the flow of the fluid. Centrifugal water or air pumps may often be strongly influenced by the impeller. For example, without limitation, varying the impeller diameter of a centrifugal water or air pump may act as a factor in reducing energy usage where loads constantly fluctuate.
Current centrifugal water or air pump designs typically use fixed diameter impellers with variable speed electric drives and motors to vary equipment speeds based on actual load conditions. Fluid moving devices with impellers that have a fixed diameter typically involve relationships between flow, speed, resistance, power and diameter based on pump affinity laws that are derived from the basic principles of fluid mechanics that use the method of dynamic similitude. This essentially means that the forces acting on the fluid, such as, but not limited to, inertia and viscous or friction forces, remain in the same proportions as operating conditions change. One pump affinity law in which an impeller diameter is held constant states thatF1/F2=S1/S2,R1/R2=S1/S22, andP1/P2=S1/S23,where F equals flow, S equals speed, R equals resistance, P equals power, and D equals diameter. If an impeller may vary its diameter as speed is increased or decreased, the power formula above can be revised by adding the relationship between varying impeller diameters to the fifth power, and this pump law becomesP1/P2=S1/S23×D1/D25.
Pump selections for heating and cooling systems for larger commercial sector buildings are usually selected for maximum design flow conditions and are often oversized for their service. Maximum design flow typically does not occur very often. The majority of pumps in most buildings employ variable flow water systems that operate between 65% and 70% of their maximum flow condition most of the time and are equipped with a variable speed drive for energy conservation. Since it is normally not possible to accurately calculate piping system resistances completely due to workmanship in installation, piping roughness affected by manufacturing, and other factors, pumps are usually selected with operating points in a region of the pump manufacturer's curve where the efficiency is held fairly constant. Otherwise, dynamic similitude in flows may not be achieved, and the predicted values will most likely be incorrect when using the pump affinity laws.
In many applications, the effect of reducing the impeller diameter of a water or air pump is, for practical purposes, substantially similar to that of a reduction in pump speed. As impeller diameter is reduced simultaneously with pump speed, a centrifugal water pump typically operates more efficiently and may require less electrical power. It is believed that it may be uneconomical to operate a pump at a speed far below its normal rated speed since pumps are often oversized for their service. Conversely, running a pump at a higher speed may exceed the pump horsepower capability of the pump. In practice it is typically appropriate to select a pump as close to its maximum impeller size as practical. In many cases the maximum sized pump impeller may be trimmed to suit the design conditions. One may expect that trimming a pump impeller more than 10% might cause flow slip between the impeller housing case or shroud and the pump casing, and a large loss of pump impeller diameter may lead to a violation of the pump affinity laws that are based on dynamic similitude.
By way of educational background, an aspect of the related technology generally useful to be aware of is that a currently available water pump impeller with variable impeller vanes may be cited as a constitution in which movement amounts of the respective vanes move in accordance with water pressure force. The pump impeller design in this approach utilizes a single torsion spring and plate cams to bias impeller rotation and a balance structure for stability. In typical use of such pumps, as engine speed increases, pump impeller speed and water pressure also increase. When this happens, the elastic force of the single torsion spring may move all of the vanes of the impeller inward by a plate cam to reduce the impeller diameter to typically decrease flow. At low engine speeds, the torsion spring may move all of the vane bodies outward to enlarge the impeller diameter to typically increase flow. This approach may be used to operate a vehicle water pump as an electric water pump where all vehicle cooling circuits are no longer tied to the rotation speed of an engine but controlled by a vehicle's single-action outlet water temperature. The variable diameter water pump impeller may vary flow as required by the temperature of the cooling circuit while the pump electric driver can be of the constant speed or variable speed type depending on the size and type of engine.
In view of the foregoing, it is clear that these traditional techniques are not perfect and leave room for more optimal approaches.
Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale.