4  FM quick reads on HVAC

1. Be Aware Of Factors That Cause HVAC Performance To Slip Over Time

Today's tip from Building Operating Managementcomes from David P. Callan and Kyle Hendricks of Environmental Systems Design: Be aware of factors that cause HVAC performance to slip over time.

Over time, building performance drifts out of tolerance from the original design intent. When tenant occupancy changes, equipment wears and temporary set point adjustments aren't restored, a building will perform very different operationally than it did at move-in. For these reasons, even a fairly new building that was commissioned and aligned with design intent before occupancy, may not be meeting its owner's operational expectations.

There are a few simple explanations for drift. First, the complex controls used in new installations are reliant on sensors. Sensor technology has improved in the last five years; however, these devices still require periodic recalibration and replacement. Secondly, people, both occupants and operators, are not machines. People have minds of their own and are not inclined to mold themselves into the prescribed behavior dictate in the design conditions and sequences of operation. We say that "passive buildings require active occupants" to achieve outstanding performance. But, in most commercial buildings, the opposite logic is employed. Occupants and facility managers alike want buildings to actively control themselves, so that occupants can go about their business with little or no attention paid to the building systems.

Even when the components of the system are complex, the control logic should not be. If facility staff, in response to a building occupant complaint or a change in tenancy, cannot quickly find a simple or temporary adjustment to the system, they will be forced to override the controls and deviate from the intended, and presumably optimal, sequence of operations. Considering that building occupants are customers, and the customer is always right, this happens frequently.

Some of the problems that routinely occur include: permanent temperature resets that may result in simultaneous heating and cooling or poor refrigeration performance, system static pressure increases to overcome isolated air distribution issues, automatic start/stop overrides, manual locking of outside air dampers, disabling energy conservation control features, non-functioning sensors, previously unknown control device and valve failure and improper installation of components.

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This has been a Building Operating Management Tip of the Day. Thanks for listening.

Boiler Safety Devices Require Operator Attention

Today's tip from Building Operating Management comes from James Piper, contributing editor for Building Operating Management and Maintenance Solutions magazines: Three boiler safety devices require operator attention.

The safe and efficient operation of boilers and domestic water heaters is essential for the smooth operation of most institutional and commercial facilities. Improvements in designs and control systems have made today's units safer and more efficient than ever.

All boilers and domestic water heaters have a range of built-in devices to help ensure their safe operation. Like other components of building mechanical systems, they require periodic maintenance to ensure proper operation. Boiler operators and technicians should pay close attention to three key safety devices to protect personnel, equipment, and the facility:

Safety valves. The safety valve is the most important safety device in a boiler or domestic hot-water system. It is designed to relieve internal pressure if a range of failures occur within the system. Although it is simple in design and straightforward in operation, something as simple as corrosion or restricted flow within the valve and its related piping can affect its operation.

Water-level control and low-water fuel cutoff. Many systems combine these two separate boiler-safety functions into one unit. They are designed to ensure the water level within a boiler never falls below a predetermined amount. Should that situation occur, the system is designed to shut down the boiler by cutting off its fuel. Proper functioning requires operators to make sure no build-up of sludge or scale exists within the system that would interfere with its detection and operation.

Water-gauge glass. Even with a functioning water-level-control system, operators must verify the actual level of water in the system. Here, too, a build-up of sludge and scale can give false level indications.

This has been a Building Operating Management Tip of the Day. Thanks for listening.

Energy Model Shows Economic Value of High-Performance HVAC

Today's tip from Building Operating Management comes from Jeffrey L. Heiken of KlingStubbins: An energy model shows the value of high-performance HVAC systems.

An energy model is a design tool that goes beyond basic computer calculation needed to select equipment sizes. Many energy modeling software packages are available. The model electronically captures all design elements, from building skin to chiller selections, and simulates building operation. Information on occupancy and utilization, space temperature settings, lighting schedules, ventilation requirements, and utility rates all serve as inputs to the model. The software then uses solar and thermal weather data and predicts needs for the building in its specific location for each hour all year. The model produces load profiles and energy demands as well as operating cost for each utility in the simulation. The estimates from these energy models, though still estimates, have shown high levels of accuracy and, as input to life-cycle-cost analyses, serve very well for comparative analysis of systems and options.

Using the energy model, design of high-performance HVAC systems should start with the overarching goal of efficient resource use. The first step is to rightsize the delivery systems. Oversized equipment, piping, ducting, motors, pumps, chillers, air handlers, etc., can add significant operating and first costs. What's more, there is the cost of added floor, shaft or plenum space for the HVAC system.

In the end equipment has to be selected. Unitary device energy efficiency ratings have improved, but how systems are set up can drive performance. Thus, high-performance HVAC systems also seek to maximize elements like economizer hours of operation, heat recovery and other elements such as thermal storage.

This has been a Building Operating Management Tip of the Day. Thanks for listening.

Repair A Pump, Or Replace It?

Today's tip is to know when it's time to repair a pump or to replace it. The first step is to understand its performance level. High-efficiency pump systems are designed for specific applications such as water treatment, condensate return, boiler feed water, chiller water in closed systems, water towers in open systems, and chemical proportioning.

Managers and technicians have a number of tools and tactics to gather essential data on pump performance. Technicians can compare baseline readings to subsequent readings to check for wear of the impeller, casing wear plates, and wear rings. Low or erratic pressure differences can indicate loose belts.

Managers must consider both in-house maintenance capabilities and company policy. Some managers opt to repair as long as the pump casing remains in good condition, which can be decades. Technicians simply replace rotating or worn parts as needed, and depending on the in-house maintenance shop, they may be able to make many of the needed parts.

One approach is that optimum service life occurs when cumulative maintenance labor and material costs equal a pump's replacement cost. Managers can use a formula to calculate a pump's optimum service life in hours and can compare optimum hours to actual operating hours.

An hour meter or service-hours recorder attached to the pump can help accurately determine actual hours. The service recorder is the best option because it accumulates operating hours and sorts them into idling hours and hours under load — valuable data for evaluating the effectiveness of the pump design. When actual hours exceed optimum hours, the unit is replaced. Company financial policy also affects the repair-or-replace decision. Managers must expense parts for rebuilding in the year purchased, but they can capitalize and depreciate replacement pumps over several years. With either option, managers need to watch for upgrade possibilities to newer, more energy-efficient designs. Upgrading the design of a pump or drive can help defray the upfront costs through energy and reliability savings.


HVAC , sensors , calibration , controls

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