Tech Topic: Optimizing commercial hydronic system performance
Today, it's all within the realm of possibility.
Boiled down to its very essence, the most exciting shift in the science of building-system design is the ability for all parts of the system to interact, combining as one to optimize system performance, comfort, IAQ and energy efficiency.
Today, it’s all within the realm of possibility.
Arguably, hydronics remains at the top of the list – where it’s been for decades – when building owners and designers consider the type of system that delivers optimally across a broad spectrum of performance variables.
Thanks to steady advancements in technology, hydronics has improved the art and mechanics of water flow.
“If we’re to consider system function much as a cardiologist might study circulatory flow, we learn that building system performance is all about flow,” says Richard Medairos, P.E., senior systems engineer and director of commercial training at Taco.
Medairos has spent more than 30 years in the hydronics and commercial building design industries, most of them as an independent consulting engineer. What he now sees on the horizon is a future that opens itself entirely to exploration and unprecedented energy efficiency, sustainability, ease of operation and interior comfort.
According to Medairos, systems integration is something experts in our industry have worked toward for decades.
The newest dimension for commercial hydronic system performance is the merging of all system equipment, components and terminal units, the piped network, high-efficient, system-reacting pumps, and building automation systems with predictive controls based on current and future indoor and outdoor conditions.
Medairos explains one of the latest advancements has been the expanding reach of sensorless and ECM pumps.
“These pumps – without the need for external sensors — are making it possible to provide the pumping power for large heating and cooling systems with amazing efficiency,” he says.
With sensorless pumping, there are no holes in pipes for tubes or taps connecting remote differential sensors together with the pump. Also, self-sensing pump system design offers the advantages of greater accuracy for variable flow, higher energy efficiency, lower installation costs and improved system stability.
Versatility and control
Most commercial systems operate by tracking and controlling pressure differential, or Delta-P (∆P). Though larger systems may track both temperature differential or Delta-T (∆T) — the difference between supply and return temperatures — and ∆P.
“A key benefit is if we can control the differential temperature, we can make the primary heating and cooling equipment more energy efficient,” Medairos adds. “For instance, a chilled water system may operate most efficiently at a Delta-T of 12° F. If that system is controlled in the Delta-T mode, optimal performance is relatively easy to dial in.”
When designing hydronic and chilled water systems, there’s a direct relationship between the ∆T and flow. An industry adage: Double the Delta-T and cut the flow in half, applies. The benefits of an increased ∆T stretch beyond a reduced need to burn fuel at the heat source. Reduced flow means being able to use pumps of lesser size while still meeting the need and the down-sizing of piping, fittings, valves and other components as well. The right choices up front can lead to a more frugal system layout and significant savings. Medairos adds that even with a traditional Delta-T operation for a hydronic system, simple variables can toss a wrench in the works.
“The ideal Delta-T for a hot water baseboard system is 20°,” he says. “But, if a condensing boiler is used, a better Delta-T may be 30° or more to assure robust condensation within the boiler.
“Yet, some systems or terminal devices may not operate as effectively with the higher Delta-T because of their design limitations or the types of control valves used where varying flow — by operating with a Delta-P mode — may improve overall system performance.
“The challenge when retrofitting equipment instead of designing systems from scratch is that not all current systems were built to operate in a Delta-T mode, so it’s best to have pumps and controls that can respond to either method of operation: Delta-T or Delta-P. The more versatile the system components, the greater the range of control system designers have; the greater the level of operational efficiency.”
“To make the primary equipment more efficient, we need to control the Delta-T and also to match capacity with the load,” Medairos states. “That’s where variable speed pumping makes its greatest contribution.”
When there’s equilibrium between a system’s capacity and load, and optimal Delta-T, maximum efficiency is attained. Medairos refers to it as a symbiotic relationship between the system and primary equipment.
“To achieve greatest performance, they need each other in a harmonious fit,” he says. “With new and responsive pump technology we can now strive for optimal system balance.”
Boldly going into a new and exciting operational realm is now the Holy Grail for system designers. After all, highly-efficient equipment and individual components — if not matched through the aegis of optimal system design – invariably contribute at less than peak performance.
“We need synergy between the central plant — whether it’s a chiller or hot water system — and the terminal equipment, and all parts in between them,” Medairos says.
A key driver is the rapidly-growing use of variable-speed pumps in the hydronics industry. There are substantial benefits:
• If the load varies, there’s a corresponding reduction in pump speed; with a drop in pump speed there’s a significant reduction in pump power (at half speed, only 1/8 of the full horsepower is required; or, by reducing speed to 1/3, power is reduced to 1/27th);
• With variable speed, power is gradually increased; soft-starts are beneficial to the motor, pump and system components; and
• By reducing pump speed to match the load, energy is saved and equipment longevity is greatly improved.
According to Medairos, if a motor rotates at 1,750 rpm, it’s x 60 for 105,000 cycles per hour x 24 x 365 = 919,800,000 cycles per year. Cycles are proportional to speed; at 1/2 speed, cycles are dropped by one-half, substantially reducing component wear, including bearings, mechanical seals, wear rings and shaft sleeves.
“Assuming the pumps perform optimally, system designers can configure systems with precisely prescribed Delta-Ts to take exact advantage of all the work a boiler or chiller can do,” Medairos states. “This means lower operating temperatures, higher Delta-Ts and terminal devices with more surface area — something that assures a lifetime of savings.”
The stage is set
The system designer’s next interest may be specification of a control system that assures the right system temperatures and flow rates to maintain optimal performance under all conditions.
With the right building automation system in place, all facets of the system are designed to work in unity. Terminal devices with sufficient surface areas assure high Delta-T’s and this translates to healthy advantages back at the central plant. Matching the variation in system loads is an issue of maintaining proper flow — there’s no better, more fitting challenge for modern pumps and BAS controls.
The final component is a system “barometer” or diagnostic window — closely tied to the control system — that allows operators to observe energy use (and savings) in real time.
Advanced building automation systems permit this, combining contemporary management of all-system operation and diagnostics with predictive controls based on current and future indoor and outdoor conditions.
An example is a system that provides dynamic graphical interface for remote monitoring of pump and system performance in real time, complete with fully-automated BAS integration. It avails automatically-rendered graphics that show pump performance, all system influences, energy consumption and energy saved in real time time, as well as automatic alarming, trending capability and even predictive maintenance scheduling.
A key advantage is the installer’s ability to see all facets of system performance, and if adjustments are needed they then have the ability to easily balance pump curves to precisely fit system resistance. This greatly reduces system balancing and commissioning time while moving that capability to the installer instead of to an expensive add-on control or commissioning agent.
For instance, in a chilled-beam system it is common to monitor supply air temperature separate from the air-handling unit’s dedicated controller. The key advantage is that system operators have predictive control of relative humidity beyond the terminal units — allowing faster reaction to changes to provide more stable and comfortable indoor space conditions.
“Having to wait for a thermostat to tell you that there’s a comfort issue in a room or rooms is simply too late,” Medairos says.
The crusade for total system efficiency is one that system designers embarked on decades ago. Invariably refinements will continue to improve performance though, unquestionably, an important plateau is now achieved. Recent Department of Energy initiatives have assigned efficiency ratings for a wide range of equipment and components, but not for combined system efficiency. Systems experts are now moving the industry toward greater recognition of loftier goals, pushing toward what Medairos refers to as “total system integration.”
“The system approach is a bit like holistic medicine,” he says. “Rather than treating a single symptom with no consideration for the whole body, some doctors prefer to treat the whole person (or system) – body, mind and spirit. Similarly, we can now design, rebuild and rate systems for optimal performance — system health — because we have the means to achieve proper balance and extreme energy efficiency.”
This article was originally titled “ More than efficiency” in the October 2015 print edition of PM Engineer.