Two-Pipe Fan Coils Get Four-Pipe Benefits
Today's economic realities force all building owners to challenge old notions of what is desirable and acceptable in HVAC systems.
Faced with mounting pressures to control HVAC system costs without sacrificing features or quality, contractors are looking for good alternatives to satisfy customer needs, stay within the system design requirements, and control costs. One such solution may already be staring us in the face: hydronics.
Over the past few years, there has been renewed interest from building owners and developers in using hydronic fan coil systems due to their application flexibility, plus their high level of zone control and comfort.
Recently this increased interest was further stimulated by the introduction of SureFlowÂ® hydronic fan coils, designed and manufactured by International Environmental Corp. (IEC).
Consequently, many building developers, owners, architects, and engineers have been changing their minds about how and where hydronic fan coil systems can be applied.
For years, hydronic system fan coils have been thought of as best suited for large building applications, where more customized features are often desired.
So, even though hydronic fan coil systems were a good choice for system flexibility and comfort reasons, many engineers and contractors were hesitant to propose them due to perceived design and installation costs.
In the congested world of contracting, more than ever contractors are feeling the pressure to set themselves apart from all the other bidders, to win the job with an attractive, innovative HVAC system while still keeping costs in check.
That's where SureFlow hydronic systems become not only a great choice for their customers, but a great business opportunity as well.
The Product's EvolutionThis new hydronic fan coil system evolved from the demand for a flexible alternative to other systems. IEC concluded that by more efficiently utilizing piping systems and by decentralizing pumping requirements, it could offer a system with installed cost reductions. The system could also reduce operation, maintenance, and life-cycle costs in both new and retrofit applications.
The system is comprised of customized, independent fan coils, and matched, factory-installed, low-wattage circulators that provide constant and predictable flow, and consequently, predictable performance. Each coil circuit (cooling and heating) has its own matched circulator. The specially designed coil and circulator eliminates the need for engineers and contractors to try to predict flow and performance, such as would be the case if each component were chosen individually.
Engineers can select single units and contractors can install single units without worrying about component matching problems, the manufacturer says. There is no need for system balancing.
Each SureFlow unit responds to the call for heating or cooling from a standard room thermostat that activates the appropriate circulator and provides a flow of cold or hot water through the coil circuit. Each zone's load requirement is satisfied by the dedicated unit, the company says.
The unit is connected to the central plant chiller and/or boiler through a network of single-pipe loops, one for heating and one for cooling (both capable of operating at the same time), or a single loop for changeover systems.
The hydronic fan coil concept further simplifies the system and substantially reduces the system's installed cost by using the same loop to provide water to the units and return it to the chiller and/or boiler, the company explains.
The circulator draws either hot or cold water on demand from its respective central loop supply pipe, pumps it through the coil, and returns it to the same loop, blending it with the greater water flow from the loop.
This causes a gradual and slight change in the loop water temperature during operation, and can reduce the amount of insulated piping to be installed by more than 40 percent, the company claims.
The Big AdvantageThe same heating-cooling versatility provided by a traditional four-pipe fan coil system can be achieved with only a two-piping system, the company says. A simple heat-cool changeover system will operate on a single pipe loop as opposed to two.
With conventional two- and four-pipe systems, water is forced through a terminal unit (fan coil) by a central water pump sized to overcome all friction losses, including the distribution piping, control valves or other balancing valves, and static losses, thereby wasting energy. Simplified distribution piping prevents balancing and control problems that are commonly encountered with multiple parallel circuits in two- and four-pipe, direct- and reverse-return systems.
With the SureFlow system, the units are hydraulically isolated from one another and are decoupled from the distribution loop. These operate like mini secondary loops. The starting or stopping of water flow to any number of SureFlow units does not inhibit the performance or control of other units; nor does it alter the steady-state flow of the single-pipe distribution loop.
By decoupling the fan coil from the loop and providing each unit with its own low-wattage circulator to control the water flow, the central pumps' required size is also drastically reduced, thereby lowering the size and cost of the pump and decreasing operating costs.
The piping systems can be designed using IEC's software and design guides. SureFlow units are selected based on types of units needed (ceiling horizontal, vertical stack, or console type) and specific zone load requirements, just as fan coils are.
Units are attached in series to a loop until all requirements are met within an area or block. With the help of the software, loop pipe sizing is calculated according to block load requirements or constraints imposed by the designer.
The designer must know such information as entering water temperature (EWT) at the beginning of the loop, maximum water flow rates (also known as flow per second [FPS]) for the loop, and peak space load and block load requirements. The loop water's thermal dynamics are automatically calculated when units are added to the loops, thereby giving the designer sufficient information to select additional units and confirm their performance.
With additional design software, distribution mains can be sized; pumps, chillers, and boilers can be selected; and other system components can be added.
Diversity FactorsIndividual loops can be easily designed to maximize diversity, the manufacturer says. Because each individual unit is chosen to accommodate the actual load requirement of the space, each unit is rated at high-speed fan and full capacity, and the loops are sized to accommodate the loop block load.
As soon as units begin to cycle off or fan speeds are reduced to medium and low speeds, the extra benefit of diversity in the SureFlow system is realized. If the total individual peak demand load of each space on a loop is compared to a separate load calculation done for the entire block load served on the loop, the possibilities of diversity within the loop are evident.
For example, morning loads differ from afternoon loads. Inasmuch as each unit is sized to meet its peak load requirement, it is highly improbable that all of the units in a well-conceived loop will be required to perform at peak demand at the same time.
The installation process for this new system requires no special expertise above and beyond what most contractors involved in hydronics already have, the company says. Because pipes rather than ducts are used, and because the pipes can be cut offsite and delivered to the jobsite ready for assembly, installation costs and on-site time requirements may be dramatically reduced.
Because each loop pipe diameter is uniformly sized, the cost of fittings and commensurate installation costs can also be reduced. Intricate valve packages are eliminated and controls are simplified. With this less-complicated, less-time-intensive installation, the company says no new training is necessary for field personnel.
An impressive feature is the low maintenance cost of the SureFlow system. The circulators are custom designed for the application and have an integral check valve and condensate baffle. They are water-lubricated and maintenance-free with no seals or bearings. The units are self-balancing, the company says; only the loops need to be balanced. Should it be necessary to physically decouple a unit for repair or maintenance, the company says there would be no adverse effects or rebalancing required on any of the subsequent units in the loop or system.
In traditional two-pipe systems, the mains are hydraulically tied to the fan coil or other terminal unit circuits, like VAV boxes. A change in flow to any of the circuits causes a change in pressure differential to all circuits, which causes consistent flow to all loads to become a challenge. To maintain flow in two-pipe systems, the engineer may elect to use three-way valves or variable-pumping technology, thereby in-creasing cost, complexity, and potential energy loss.
As they say, everything old is new again. Hydronic heating and cooling has been a favorite for decades due to its performance and comfort. Now it has become a favorite for its flexibility.
This article was provided by Rick Bostian of International Environmental Corp., SureFlow marketing manager. He may be reached at 405-605-5139 or www.iec-okc.com.
Publication date: 02/07/2005