Choosing the right pump is essential for optimised HVAC design

By Ghida Kaddah, mechanical design manager at Khatib & Alami

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Ghida Kaddah, mechanical design manager at Khatib & Alami.
Ghida Kaddah, mechanical design manager at Khatib & Alami.

The human body consists of many different components which work together in harmony to keep us alive. The heart is the engine that pumps blood to our organs and tissues, and ensures that oxygen, nutrients and hormones are relayed to our cells to sustain us and remove toxins and waste products.
In much the same way, HVAC pumps are an integral component in most centralised HVAC systems. HVAC pumps are essential in boilers, cooling towers, chillers and more; and while many dramatic advances have been made in most elements of the HVAC system, the guiding design principles of pumps has remained relatively unchanged, apart from innovations around more advanced selection tools and intelligent pump controls. To ensure optimised HVAC design, the designer has to make sure that the selection of the HVAC pump is optimal to its application and properly sized, tested and commissioned.

There are many types of pumps used in fluid transfer but the most common are centrifugal pumps which may be end suction, vertical inline, horizontal or vertical split case. Depending on the flow and the head, the designer will choose the appropriate type. For example, for relatively smaller flows up to around 1,500 gallons per minute (GPM), it makes more sense to select end-suction, while for higher flows, vertical or horizontal split case is a better choice, both economically and technically.

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Properly sizing the pump requires the designer to calculate the flow of liquid needed, and against what pressure (head). After these figures are determined, variables such as fluid type, temperature and density are inputted into a selection software, in addition to one of the aforementioned pump types.
A critical issue with choosing the right pump is to consider its best efficiency point (BEP), defined as the flow at which the pump operates at optimum efficiency for a given impeller diameter. Typically a pump’s efficiency is around 60-80%, and the selected pump should have its BEP at around 10% of its design operating point. Another factor to consider is its revolutions per minute (RPM). Generally speaking, the lower the RPM the better; however there is an increased cost factor to using a lower RPM pump. Another critical issue to consider is choosing the right material for the pump, mainly corrosion-free material due to the harsh climatic conditions, high ambient temperature, humidity and salinity in our region.

Variable frequency drives (VFD) in HVAC pumps adjust the speed of the pump motor based on demand, thus saving energy and prolonging the pump’s life. If the pump has variable flow conditions, then a VFD can provide better energy savings than mechanical means and potentially reduce total system costs. In addition to energy savings, they reduce mechanical stress on the pumps and pump systems, resulting in longer life and reduced downtime/reliability issues. Encouragingly, clients are taking note of this and the use of VFD pumps in HVAC systems has become widespread in the GCC market. 

Procurement and commissioning is the last step after the pump is sized and selected. In the GCC, a trend has emerged where contractors are suggesting to clients and consultants, as part of the tender queries and value engineering exercises, to scrap factory testing for HVAC pumps. While this approach may save money in the short-term, we don’t recommend it because factory testing of pumps is crucial and certifies that the procured product meets the highest performance standards.

The way ahead
Smart technologies continue to shape the future, helping to tackle some of the biggest challenges facing the world such as climate change and energy conversation. In our industry, smart technologies are disrupting many of the old ways of construction and engineering. This can be seen in the buildings sector, where advances in HVAC pumps are making buildings more energy efficient and user friendly. For instance, electronically commuted motors (ECM) for small centrifugal pumps prolong the life by varying the flow to match the demand, coupled with a complex built-in control logic that adds flexibility and guarantees the operator’s specific needs are met. Moreover, cloud computing has allowed pump operators to store and analyse vast amounts of data which can be particularly useful in rectifying problems such as minor out-of-tolerance readings in a pump’s set point, speed, temperature or other variables.

Advanced selection tools are now available online which help designers to choose the right pump for the right application. And with governments keen to reduce electrical energy usage in the HVAC industry through incentives and regulations, it will become imperative for designers to implement smart technologies and robust testing and commissioning for HVAC pumps.

Very soon, we can expect to see more advanced commercial and industrial water pumps come on stream in the US. From February next year, a US Department of Energy (DoE) ruling comes into force that requires all pumps that operate between 1 to 200 horsepower to meet a set efficiency standard or Pump Energy Index (PEI). The new PEI is intended to minimise the nation’s energy consumption, with the DoE estimating that 0.29 quadrillion British thermal units (BTUs) will be saved between 2020 and 2049, which translates into a savings of about 10 gigawatt-years of electricity.

In this region, we are seeing some advances in HVAC pumps brought about by governments and clients wanting to reduce energy consumption in buildings. Dubai Supreme Council for Energy, for instance, wants to reduce Dubai’s electricity and water consumption by 30% by 2030. This is helping to drive the shift from engineers using constant speed pumps in favour of variable frequency drives (VFDs) in HVAC systems.

According to forecasts from Navigant Research, the market for commercial, energy efficient HVAC technologies will reach $61.2bn in 2027, mainly owning to regulations which encourage commercial building owners to adopt smart controls for intelligent management and building operations. One such technology is smart energy metering for variable refrigerant flow (VRF) air conditioning systems. VRF systems use refrigerant as the means of cooling, with the option of providing for multiple indoor units working with one outdoor VRF unit. The refrigerant flow will vary and be able to cater to the individual needs of the indoor units. These systems offer ease of installation, design and a portfolio of products from leading manufacturers, but their use was restricted to villas and single owner establishments up until now.

Recent developments in smart energy metering, however, such as the introduction of the power proportional distribution (PPD) option by Daikin and the power distribution indicator (PDI) by LG, now allow the owners of multi-tenant buildings to take advantage of VRF technology. Tenants will be charged based on an allocated amount of power used by the outdoor portion of the unit. A developer we are working with has been so encouraged by the benefits of VRF energy metering that they have made their use part of their strategy for all projects moving forward.

Without doubt, we are living in an era of rapid change and innovation, with smart HVAC technologies set to play a huge role in making buildings more energy efficient. It is incumbent on engineers to be on top of these innovations so we are able to recommend them to clients and integrate them into our designs.

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