By Keith Sanders, PIA Councillor and Life Member
The Australian Building Codes Board (ABCB) is in the process of revising the energy efficiency provisions in Section J of the National Construction Code (NCC). One area the review will look at and where energy efficiencies can be realised is HVAC. Here, we’ll look at the proposed revisions for the selection and design of HVAC systems in relation to pumps, and how these changes will impact the sector if implemented.
The project stems from Measure 31 of Council of Australian Governments’ National Energy Productivity Plan, where the ABCB was requested to consider changes to the energy efficiency provisions for NCC 2019 in December 2015.
In April 2017, Energy Action approached Pump Industry Australia (PIA) to assist with a review of draft recommendations to the ABCB in relation to pumps used in HVAC systems, resulting in a revised report in August 2017 with some of the PIA recommendations included.
The report submitted by Energy Action focused on how the methodology for pump selection can be improved to achieve better pump and system matches that will lead to lower power consumption and improved equipment reliability.
Looking for ways to improve
To help with Energy Action’s review, the PIA Council approved the formation of a small sub-committee to investigate how pumping equipment in HVAC specifications is currently specified. The aim was to propose a methodology for ensuring the industry follows best practice in the design of HVAC systems to minimise energy losses and the selection of appropriate pumps, motors and control systems.
The sub-committee worked to prepare a practical recommendation based on the products known to be available in the Australian market. In addition, the PIA’s relationship with the British Pump Manufacturers’ Association (BPMA) allowed access to the latest information from Europump to determine if this could be adopted in Australia.
This included a detailed look at end suction pumps in the ISO 2858 range and the EN 733, used extensively in this market sector and consideration of a minimum energy performance standards (MEPS) approach to these product ranges.
Considerations for review
The sub-committee looked at the issues that need to be addressed to promote the minimisation of energy consumption in HVAC systems. While this requires a “system approach” to achieve the maximum benefits, there are also benefits in proposing the use of products that are in the upper levels of efficiency by adopting MEPS approaches for pumps, motors and control systems.
- Good system design is the responsibility of the HVAC contractor and sizing of pipework is a significant factor in minimising friction losses in the system. Limiting flow velocities is the preferred approach with 2-3 m/sec considered a reasonable target
- Determining the principal pump duty needs to be undertaken carefully by HVAC contractors once the final system design is completed. Pump suppliers should be provided with sufficient information to allow for the optimum pump selection. A better understanding of the preferred operating region (POR) on a pump curve needs to be promoted by using the “house of
efficiency” approach. Flow rates below 75 or above 110 per cent of BEP of the proposed pump should be discouraged
- The level of confidence that can be placed in the information contained in pump curves needs to be better understood. Pump curves used should comply with AS 2417-2001 or AS/ISO 9906 2018 (currently being processed by Standards Australia) and this should be stated on the contract curve
- Where variable flow demand is envisaged, a load profile will assist this process and provide a basis for flow control selection. The costs/benefits of variable speed drives should be more rigorously analysed and control systems selected appropriately
- Installation and commissioning of pump equipment is an important step in determining the pump and system match to ensure the pump is operating in the preferred zone
Reviewing best practice for HVAC pump selection
In creating the recommendations, the key issues surrounding the design, selection and putting into operation of pumping equipment used in the HVAC sector was looked at.
The importance of system design in the pump selection process
The initial system design is often influenced by the mechanical services consultant, who issues a performance specification. This allows for HVAC contractors to submit proposals for packages of equipment based on the building design, the level of heating or cooling required, and the major items of equipment that will be required to satisfy the performance specification.
HVAC contractors usually issue a specification to pump suppliers who will provide quotations for pumping equipment. At this stage, the information provided to pump suppliers is often very limited. The nominal duty may not be particularly accurate and may also contain contingencies that might result in a significant over-estimation of the flow and head requirements.
While this might provide a level playing field for comparison of pump proposals, it can often result in pumping equipment being “oversized” for the final installation.
Once an HVAC contract is awarded, it should be the role of the successful contractor to re-calculate the pump duty based on ultimate combination of major equipment, positions of key plant within the building and the size/material of the interconnection pipework.
There are likely to be a variety of systems to consider, but usually these fall into one of two main categories:
- Closed loop systems – In such systems, the static head is zero and the friction losses relate to losses in the major items of equipment and the friction losses in the interconnection pipework. The sizing of pipework is important because losses increase as pipe size decreases. For this reason, it is proposed to limit flow velocity in pipework to 2 to 3 m/sec. The shape of the system curve will follow a square law for the origin
- Open loop systems – In such systems, the existence of static head is likely and the shape of the system will be somewhat different. Static head will exist at zero flow, while friction losses will increase as flow increases. It is helpful in the pump selection process to know the estimated static head. Again, pipe size is important and should be selected to minimise friction losses within reasonable cost limits
Determining the nominal (predominant) pump duty
Ideally, the pump supplier should be provided with an updated estimate of the nominal duty that the pumping equipment should have to satisfy. This should include:
- The revised estimated system curve
- Any overload or partial loads to be accommodated (preferably in a load profile)
- Any mechanical/electrical conditions or constraints imposed by the consultant specification
- Any special conditions for electric motors or drives should be specified. MEPS compliant motors are available in Australia and can be fitted to long-coupled units relatively easily. Motors fitted to imported close coupled pumps should also be checked for MEPS compliance
This should result in a much more accurate proposal for pumping equipment and allow for pump selection close to best efficiency point (BEP) in all operating conditions.
The pump supplier should also be notified of any changes in major equipment in the HVAC circuit or pipe runs that might affect friction losses that occur during the construction phase. This will help inform if any changes to the pump configuration are required to achieve a satisfactory pump and system match.
The operating point of a pump is determined where the pump curve crosses the system curve. The pump produces only enough energy to overcome the system resistance generated and the actual flow and head are a result of this balance. The operating point is important for two reasons:
- It should be as close as possible to the pump’s BEP to minimise power consumption
- All operating points (including partial and overload conditions) should be within the POR to minimise unstable operating conditions which may affect the operating life of critical components
- As a guideline, the POR might be for flow conditions from 75 to 110 per cent of BEP flow. The use of variable speed drives to more accurately achieve a pump and system match at the commissioning stage is not a preferred solution unless partial and overload conditions fall outside the preferred operating range
Understanding pump performance curves and selection data
Most pump manufacturers provide pump performance curves or other data that will indicate the flow (Q), head (H), power absorbed (P) and pump efficiency at various impeller diameters and speeds. However, as most standard pumps are mass produced, the pump performance is subject to tolerances, as manufacturing variances are inevitable.
Most curves will also provide information on the net positive suction head required (NPSHR) demanded by the pump to operate satisfactorily, although in most cases this is not a major issue in HVAC applications.
The H-Q curve for a pump is really an “energy versus flow” curve. The energy consists of kinetic energy and potential energy which the pump imparts to the fluid as it leaves the pump casing. This energy (normally expressed in metres head) will allow the pump to overcome the total system head generated at the duty point (also expressed in metres head).
Published pump curves are still used extensively in pump selection procedures, although many of the major pump suppliers can also provide computer selection programs to assist in the pump and system matching procedure. Special care needs to be taken to understand the level of confidence that users can place in the accuracy of the pump performance data.
Published pump performance curves are generally based on manufacturers test data performed to a nominated standard. In Australia, the current test standard is AS 2417 – 2001. This is directly equivalent to ISO 9906-1999. Most published pump curves nominate they are valid for mass produced pumps and claim Annex A tolerances.
However, it is unlikely any contract pump will have been subjected to a performance test, unless the customer calls for this to be undertaken. This is not common in the HVAC sector. As a result, the reliability of data in the published curve is only verifiable if the test code is clearly nominated and the tolerances can be assessed.
Any test data will relate to a specific pump configuration being tested and in most cases the pump will be set up in the standard material configuration. Until recently, the standard material configuration for larger end suction pumps was:
- Casing: Cast Iron
- Impeller: Gun Metal or ZF Bronze
- Shaft: Stainless Steel (SS416 or SS431)
However, in recent years some suppliers have chosen to supply cast SS impellers and this sometimes has an impact on the seal ring clearances, which results in a de-rate of pump efficiency.
In summary, the accuracy of the pump curve should be assessed based on the limitations that must be clearly defined on the curve. Computer generated curves from manufacturers selection programs should also have the limitations on their validity specified in the event of any potential dispute on performance when the pump is commissioned on-site.
Flow variation/control strategies
Many HVAC systems require a constant flow for most of the operating period. The control system is relatively simple and often the control parameter is “temperature”. In such cases an accurate pump and system match will allow for stable operation at a duty near to BEP without speed control.
However, more sophisticated systems result in more complex operating conditions and variation is more effectively managed by speed control to reduce energy consumption at partial flow conditions.
It is helpful to pump suppliers if system load profiles and control system strategies can be made clear at the time the equipment is ordered, as retrofitting more complex equipment can often result in high additional equipment and installation costs. Guidelines for the effective use of variable speed drives (VSDs) should be outlined in the new code.
Pump performance testing and pump site commissioning procedures
Depending on the anticipated hours of operation and the size of the drive, consideration should be given to performance testing of pumpsets prior to installation at site. This will provide a verifiable basis for actual pump performance and allow for more effective problem solving at the site commissioning phase.
While AS 2417-2001 is still current, PIA has made a submission to Standards Australia to adopt the latest ISO 9906-2012 as the applicable standard for Australia. It is expected this will be adopted early this year, resulting in AS 2417-2001 being superseded by AS ISO 9906:2018.
While there are other testing codes used in other industry sectors, the new standard is adequate for the HVAC sector if correctly applied.
At this stage the recommended tolerances for pump testing should be as follows:
- Pumps tested to AS 2417:2001 – Grade 2 – Use Annex A tolerances
- Pumps tested to AS/ISO 9906:2018 – Grade 3 – Use 3B tolerances
Site commissioning of pumps in the HVAC sector should be undertaken by qualified personnel. This is a very important stage in the lifecycle of pump equipment and very often the only time when it is possible to determine if the pump duty provided to the pump supplier was correctly assessed.
Temporary or permanent instrumentation may be used to measure pump performance and assess both pump power absorbed and pump efficiency at the operating point. This initial site testing provides baseline data for any corrective action to be undertaken to optimise performance and subsequent assessment of any drop off in pump performance over time.
It may not be unusual to find that the site operating point is not an exact match for the duty nominated for the pump. There are several reasons for this and a careful investigation needs to be conducted to determine the causes for any deviation. At this point, an actual pump test curve is very useful, as it should have been undertaken under specified conditions that may not be reproduced on-site.
This is also an ideal time to undertake an energy audit of the equipment. Again, this needs to be undertaken by a qualified professional. Energy conservation is becoming a global issue and measures that encourage a long-term approach to pump and system design are likely to achieve a good outcome if correctly implemented.
A systems approach to HVAC
A “systems approach” has the capacity to yield significant energy savings within HVAC installations, providing the exchange of information between all parties involved is comprehensive and efficient.
The situation in Australia lends itself to the adoption of European guidelines for circulators and this has been accepted by Energy Australia in its recommendations to ABCB.
However, it is possibly too early to adopt the Extended Product approach which is currently being adopted in Europe and in the short term a MEPS recommendation for ISO 2858 and EN 733 pump ranges may be a simpler and easier methodology to adopt.
It would be logical to also adopt the existing MEPS for electric motors used in HVAC applications as this is already applicable to suppliers of electric motors in Australia.
As technology develops, there should be opportunities for further upgrading of pumping equipment specifications to yield additional energy reduction over time.
The NCC 2019 public consultation draft can be viewed at www.abcb.gov.au/Consultation/Public-Comment-Draft/NCC-2019-Public-Comment-Draft. Final changes are expected to be released in February 2019, and come into effect from 1 May 2019.