Circulating Hot and Chilled Water Pumps with Variable Speed ECPM Motors
Hot and Chilled Water Circulation: Variable Speed ECPM Motor-Driven Circulator Pump vs. Constant-Speed Pump
Speed-controlled circulating pumps for heating, cooling, and domestic hot water systems using electronically commutated permanent magnet (ECPM) motors.
Item ID: 291
HVAC--Air & Fluid Distribution
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.58 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- While not large savings potential, it would be helpful to develop guidelines for estimating and verifying energy savings, and exploring non-energy benefits.
- This lumps way too many variations. For (rare in the NW) residential hw space heating, it is on the market and needs evaluation. It may be a great solution for multi-zone systems. For service hot water in commercial buildings, I think there are several better solutions, depending on whether you're dealing with new construction or retrofits. For chilled water, I'm not sure what optimum control looks like when we can modulate everything: cooling tower fan, cooling water pumping rate, chiller compressor, supply water pump to water-to-air HX, and air handler fans. In theory it can be done, but can it be done reliably and verified easily? What tools should be developed to take much of this away from the controls designer and replace it with a "learning" system that calculates and adapts? is that where effort should go?
- These should become required by code.
- Great energy saver. Needs robust testing in the US. Is required by code in the EU but is taking a long time to catch on in the US.
Use of oversized pumps in hydronic (water piping) and radiant heating and cooling systems is common—some experts estimate up to 99% are oversized. Oversized pumps move more water than necessary and use more energy in the process, so there has been a push starting in Europe to use a different type of pump motor that can use less energy. Variable speed, electronically commutated permanent magnet (ECPM) motor-driven circulating hot or chilled water pumps can save 20% to 80% of annual pumping system energy use by only delivering as much water as needed. Reducing flow rates means that return water temperatures will be lower, resulting in improved heat transfer and boiler efficiency, particularly for condensing boilers. Pumps are available with drive motors rated between ¼ and 7.5 horsepower. These pumps are also useful for solar hot water and ground source heat pump systems.
In the past, a factory-trained technician was needed to program the pumps to supply the optimum flow rate. This task is made easier because the Grundfos ALPHA unit can be equipped with “Smart” AutoAdapt controls that will automatically analyze the heating system, find the optimum setting, and continue to adjust its operation to changes in demand. Armstrong’s Compass has a similar auto algorithm. Taco’s Bumble Bee variable speed circulator counts the number of open zones and takes outside temperature into account to provide the minimum flow necessary to deliver the required flow.
The pump and motor are sold as an integrated unit, and the variable speed drive must obtain a feedback signal from a sensor, be pre-programmed, or be equipped with smart programming to fully utilize its variable speed capabilities.
Baseline Description: Typical hot and small chilled water pumps
Baseline Energy Use: 1 kWh per year per square foot
Assume that a 1 hp fixed speed motor is used to circulate hot or chilled water for a 2,000 sf area. The pump drive motor is assumed to operate at a 75% load factor and have an efficiency at its load point of 83% (Note: Federal efficiency standards have been passed for small single-phase motors that are in effect in 2015. For a 4-pole motor, the full-load efficiency standard is 82.6% for a 1 hp motor. As this measure is for new construction, this efficiency will be assumed for a baseload, fixed-speed motor). The pump is assumed to operate for 3,047 hours annually (58.6 hours per week for office buildings, (CADMUS, 2009 Pg Table C-SC2)). Annual energy use is thus 1 hp x 0.746 kW/hp x 0.75 x (1/0.83) x 3,047 = 2,053 kWh/year. This is equivalent to approximately 1.0 kWh/sf-year.
Manufacturer's Energy Savings Claims:
"Typical" Savings: 80%
Taco claims that its Viridian hot and chilled water circulating pump ECPM motor saves up to 80% of the electrical energy compared to conventional pumps. Grundfos and Wilo also claim up to 80% savings on their ECPM motor-driven pumps.
Best Estimate of Energy Savings:
"Typical" Savings: 75%
Low and High Energy Savings: 20% to 80%
Energy Savings Reliability: 5 - Comprehensive Analysis
Assuming 45% efficiency for the existing motor and 80% efficiency for the ECPM unit, the energy savings are equal to the original energy use multiplied by (1 - E1/E2), where E1 and E2 are the efficiencies of the standard and ECPM motors at their load points, respectively. The expected energy savings percentage just for this motor upgrade is (1 - 0.45/0.8) x 100% = 44%.
Energy savings also result from the variable speed capability of the new ECPM motor, which is actually responsible for the bulk of the energy savings. Assuming an average speed reduction of 37%, the total energy savings would be equal to about 75% of the baseline energy use.
Actual savings will depend on the site-specific operating load profile.
Prism Engineering investigated the energy savings with ECPM pumps for BC Hydro, publishing the findings in a report, “New Pump Technology Pilot Project,” dated May 2009. The study compares two nearly identical high-rise residential towers in Richmond, B.C. Each building originally had a 1.5 hp constant-speed pump to serve all perimeter heating needs. In one of the buildings, this pump was replaced with a Wilo Stratos variable speed pump. Metering was installed in both buildings to measure electricity consumption for pumping. Measured power draw for the existing pump averaged 1.1 kW throughout the test period, while power consumption for the Wilo Stratos pump averaged 0.45 kW in the winter months and 0.3 kW in the spring. The researchers projected annual energy savings of 76% (Wilson, 2010).
Energy Use of Emerging Technology:
.3 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology applies to new applications in commercial buildings with chilled water systems when the pump is less than 7.5 hp. Retrofits are known to not be cost-effective due to requirements to replace existing 3-way valves with two-way valves. Estimates are based on preliminary updated numbers from the 2013 update to the Commercial Building Stock Assessment (CBSA) using the estimates for 2014. Using market shares from the CBSA (CADMUS, 2009) – the percentage of commercial space that is conditioned (85%) and served by chilled water systems (19%). The CBSA estimates the commercial building stock will grow by approximately 1% over the next 20 years. To account for additions to the building stock, use 10 years of growth to account for the potential, which is 10% of the existing housing stock. Estimates are further reduced by 75% to include only chilled water systems with motors 7.5 hp and below.
Using the market shares above results in a total potential of 3,118,000,000 sf x 0.1 x 0.85 x 0.19 * 0.25 = 12,588,925 sf.
Regional Technical Potential:
0.01 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $1.00
Baseline Technology Unit Cost (Equipment Only): $0.50
The Grundfos Magna commercial circulator pumps cost about 50% more than standard circulators. Wilo indicates that the Stratos and Stratos ECO pumps cost 200% to 250% more than standard circulators. The simple payback for these pumps (assuming electricity savings only) can range from eight months to about three years in new construction (Wilson, 2010). Note that the pump and motor are sold as an integrated unit, and the variable speed drive must obtain a feedback signal from a sensor, be pre-programmed, or be equipped with smart programming to fully utilize its variable speed capabilities.
ECPM motor-driven circulating pumps should be considered during new construction of circulating hot and chilled water systems that utilize pumps of 5 hp or less. VSD-driven pumps are already required by code for larger systems. Retrofits are not cost-effective as the three-way valve that diverts hot or chilled water from a supply line to a coil must be replaced by a two-way valve. Without this modification, pressures would not build up in the supply line to give a signal to the pump VSD to reduce speed. The cost of each “hose kit” consisting of a new valve, strainer, and pressure transmitter port is about $1,000. This requirement for valve replacements results in the simple payback for a retrofit being well over 100 years.
For new construction, costs depend on whether a cast iron or stainless steel pump is installed, and varies depending on developed head and flow. An Armstrong Compass has a power range of 5W to 45W with a first cost of $266. A 1/6 hp Magna costs $546; a 1/3 hp pump costs $1,463; and a 1 hp pump cost about $2,025 (Internet prices, March 2015). Assuming that a 1 hp pump can serve about 2000 sf of floor area, the cost is about $1/sf. Flange options can be sold separately.
Simple payback, new construction (years): 7.4
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.