Flexible Environment
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Introduction
Marflow’s 'flexible commissioning' concept opens the doors for a whole new approach to the design and operation of fan coil and chilled beam systems. As such, it enables building operators to quickly, easily and cost-effectively adjust their air conditioning systems to suit changes in occupancy or in the configuration of the workspace.
Crucially, this can be achieved without specialist commissioning skills.
Background
Traditionally, changing the configuration of a fan coil or chilled beam system, and subsequently re-commissioning the system, has been extremely disruptive and expensive. In particular, it has required specialist engineers to access the ceiling void to make all necessary adjustments, so that very often staff would have to be moved from the area while the work was carried out.
As the modern workplace has become increasingly mobile and flexible, this has proved to be a major concern for building operators. Maximum efficiency will only be maintained if the systems are adjusted each time the workspace changes, but the associated disruption and expense has often deterred people from making these changes. The result is that many systems now fail to maintain their design performance as building operators compromise and follow the path of least resistance.
In contrast, variable refrigerant flow (VRF) systems can be adjusted and re-commissioned from a central PC with no disruption and minimal expense. However, many specifiers and building operators have concerns about distribution of refrigerant within the building and would prefer to use hydronic systems where possible.
The flexible commissioning concept gives building operators comparable flexibility to VRF systems and enables them to maintain optimum performance for their systems.
Flexible commissioning
The flexible commissioning concept exploits the characteristics of addressable pressure independent two-port control valves (PICVs) and the ability to adjust these valves from a remote location through a BMS or BACnet system.
Use of addressable PICVs can be quickly and easily adjusted to suit different circumstances, creating a dynamic regime that gives building and energy managers far greater control of both energy optimisation and comfort levels.
For example, such a system enables water flows to be quickly and easily adjusted in relation to increasing or decreasing heat loads in a workspace, without the need for specialist commissioning skills. Similarly, in a situation where heating and cooling are provided by a heat pump, use of an addressable valve will enable water volumes to be adjusted in direct response to changes in heating and cooling loads throughout the year. In this way, the same coil can be used for heating or cooling for most of the year, adjusting water volumes to compensate for the varying outputs of the heat pump.
This enhanced flexibility can also help to reduce maintenance requirements. For instance, when valves are fixed at a minimal position, the orifice may be so small that dirt and air can become trapped. Conventionally, the only way to free any dirt particles larger than the set orifice is to manually open the valves to allow the dirt through. However, with a dynamic system the simple expedient of setting valves to open fully for a few seconds once a week will eliminate blockage problems by flushing through any accumulated dirt particles.
Conclusion
At a time when building operators are under considerable pressure to improve energy efficiency and reduce carbon emissions, the flexible commissioning methodology provides the tools to ensure their air conditioning is responsive, adaptable and maintains efficiency through the life of the system. It also makes it easier for them to introduce low carbon technologies, such as heat pumps, to existing systems without major disruption or expense.
The Marflow remote commissioning system allows the water side controls for hydronic air conditioning systems to be quickly and easily set into motion without needing to access the valves except for pre-commission cleaning and flushing, and for flow rate verification where needed.
The system offers dynamic balancing of variable volume water systems and full authority waterside temperature control. In addition Marflow have developed the Single Station Balancing method for verification of dynamically balanced systems, this method allows the system to be checked in both full and part load conditions.
The system comprises three elements a pair of heating and cooling valvesets, a BMS outstation controller with specialised firmware, and an interface program.
In Use
In use the valvesets operate as in any other variable volume water system, the valves modulate to vary the volume flow rate of water in relation to the demand for heating or cooling as determined by the outstation controller.
The outstation controller is programmed with a control strategy for fan coil units and is capable of modulating not only the valve position but the air side volume flow rate if EC fans are used.
Every 24hrs a valve massaging / flushing routine is launched whereby each of the valves is opened up to 100% regardless of their design position and flushed through in order to keep the valve free from possible dirt build-up. A logic routine is included such that only 1 particular valve set in any circuit launches this routine at any one point in time, thus ensuring the pump does not need to ramp up.
The valvesets include all of the control valves for each terminal unit including those needed for flushing, isolation and drain down. A rotary pressure independent control valve is used for dynamic flow limiting and temperature control, this is coupled to a rotary actuator. A flushing bypass is included for pre-commission cleaning and, if needed, a flow measurement valve can be provided.
The valvesets can be configured for close coupling directly to the terminal unit (for example above the condensate drip dray of a fan coil) or mounted in a pre-insulated box for mounting in the pipework.
The outstation controller can be configured to act as either a full coil controller or just to control the terminal valvesets. The controller interfaces a BACNET network and contains custom firmware so the connected valves can be set to any particular flow rate via the interface software.
The controller can be mounted in a self contained box complete with transformer and plugged connections for the actuator’s terminal unit and network connections.
Software
The LAPCAST interface software is used to interface with each of the controller outstations.
The software allows easy adjustment of
- VminH, VmaxH, VminC and VmaxC settings.
- Manual overrides for on-site testing and simulation.
- Local internal frost protection set points.
- Networked master/slave facilities without separate interconnecting wiring.
- Full adjustment of all control settings, including proportional bands and dead zones.
The software enables each floor/zone of FCU controllers to be easily scanned and checked for correct operation, wirelessly from a standard laptop. The software allows single mouse click functions to greatly accelerate terminal unit commissioning by addressing multiple controllers including:
- Manually start/stop the FCUs.
- Manually open/close all heating valves.
After the pre-commissioning of the pipework system has been carried out in accordance with the relevant BSRIA applications guide the water system is ready for commissioning.
"Commissioning" is defined in CIBSE Commissioning Codes A, C & W as:-
"The advancement of an installation from a stage of static completion to full working order to specified requirements.
Note 1
Commissioning shall include the setting to work and regulation of an installation.
a) Setting to work: The process of setting a static system into motion.
b) Regulation: The process of adjusting the fluid rates of flow in a distribution system within specified tolerances.
Note 2
Commissioning shall be deemed complete at the “conclusion to regulation”.
In the case of the remotely commissioned system manual regulation of the valves is replaced by motorised control of the valve’s open position. Commissioning each valveset occurs when the outstation controller is programmed with the correct flow rate via the interface software. When this value is set the valve will never open beyond the position at which design flow occurs, except when overridden or the valve massaging routine is in operation.
To commission the system the commissioning engineer connects to a BACnet router either by a wired Ethernet connection or by wireless connection if a wireless router has been included in the system. Then by means of the LAPCAST interface software each controller outstation can be addressed, uploaded with the latest firmware and programmed with the correct water flow rate.
When this is complete for every unit, the water system is commissioned.
Verification
The remote commissioning system is dynamically balanced, meaning that changes in the differential pressure within the system do not have any local effect on valve flow rates. The pressure independent control valves maintain a constant flow as long as a minimum differential pressure condition is met.
In practice this makes PICVs perfect for variable volume systems because, as the parts of the system enter part load conditions, the pump can be turned down and those valves that still have demand can provide that demand unaffected.
Current commissioning practice uses techniques derived from constant volume water systems to commission variable volume systems. Marflow have developed a method specifically for verification of dynamically balanced systems. The Single Station Balancing Method (SSB) verifies that design flow rates can be achieved under full system load and at part load.
SSB relies on the knowledge that, if sections of a dynamically balanced system are shut down, then those remaining should still supply the same flow rate.
Take, for instance, a small sub circuit containing two valves A and B. When both valves are in operation a flow rate of AB can be measured at a measuring station. If valve A is shut down then the flow rate measured at the measuring station is equal to that of B, similarly if valve B is shut down then valve A can be measured.
Marflow have developed a spreadsheet based package in order to calculate and present all the information required to perform a Single Station Balance on a particular system.
