4  FM quick reads on HVAC

1. When Sizing HVAC Systems, Focus on Proper Margin for Safety

When the HVAC system is being designed, one important decision is how big equipment needs to be. Peak demand on very cold and very hot days is one important consideration. And flexibility for change in use of a space may be another element in the decision.

Of course, there’s a price to be paid for extra capacity, and it’s not just the higher first cost of larger units. Operating expenses are likely to rise for equipment operating at part load. What’s more, larger units may very well be noisier. Properly sized units, by contrast, will likely run better, be more energy efficient and have fewer maintenance problems.

Clearly it’s important not to oversize units. But there’s evidence that does happen in some cases. One possible source of trouble is industry rules of thumb for determining occupancy when occupancy isn’t known. Those rules of thumb may lead to an overestimation of loads. Another potential problem is building in too large a margin for so-called design days, when temperatures are at their highest and lowest, so that designers have a cushion — just in case.

For facility executives, the way to avoid oversizing is to work closely with the design team to ensure that the system can handle the loads it will be facing, with an appropriate margin for safety — but not an excessive margin.

Keep the Unintended Consequences in Mind When Cutting Costs

In today’s economy, the pressure to cut costs is intense. But cost cutting moves can backfire if consequences aren’t carefully evaluated.

Value engineering is a prime example. Changes made to reduce construction costs can increase other costs. Buying windows that are less energy efficient, for example, will not only raise energy costs, but also push the HVAC system perilously close to capacity on design days.  

Higher energy prices aren’t the only risk. Design changes can affect compliance with fire safety code or inadvertently compromise security.

In a worst case, a move to cut costs could actually cost a company business. In one case, a financial firm identified a new location that had lower rental rates and was closer to home for most employees. It came close to signing the new lease, but eventually decided to stay where it was. The reason: The current location was very close to a major customer, one that was likely to be a significant source of new business in the future. The real estate savings were no reason to risk that opportunity.

It’s important to solicit input from all parties that will be affected by cost cutting moves. Doing that makes cost cutting more difficult – the parties affected are likely to put up at least a little bit of a battle – but it can save money in the long term.

Getting the Benefits of Free Cooling

Many building control systems offer facility executives the opportunity for free cooling – using the economizer cycle to bring in additional outside air rather than running the chillers. For that strategy to work, of course, the outside air has to be cool enough – typically in the mid 60s or below. When the outside air temperature falls below the low 50s, a facility may not need chillers at all.

The specific temperatures to be used for free cooling vary from building to building. One reason is that the needs of buildings are different, and so are their HVAC system designs. Another important reason has to do with outside humidity levels. Dryer air can be used at higher temperatures than air with more moisture in it.

But not all buildings that could run economizer cycles are getting the benefits of free cooling. It is possible that the controls aren’t correctly programmed. Or that dampers aren’t operating properly. It’s also possible that the temperature or humidity sensors are out of calibration. Those factors are all worth checking if the chiller is operating when the outside temperature is low enough for free cooling.

Make Sure New HVAC Systems Are Designed for Maintainability 

I’m Ed Sullivan, editor of Building Operating Management magazine. Today’s topic is the importance of keeping maintenance in mind when designing new HVAC systems.

Facility executives have a lot to keep in mind when new HVAC systems are being designed. But there’s an important point that’s often overlooked: the maintainability of the system being designed.

Good maintenance is crucial to the operation of HVAC units. Without good maintenance, energy costs will rise, and equipment will need more frequent repairs and ultimately will fail sooner. The result will be significantly higher life cycle costs.
Designing for maintainability isn’t conceptually difficult. The biggest thing is to give HVAC mechanics the space to do their jobs. Mechanics need to be able to reach valves, access hatches, filters in air handling units, and so on. Moreover, they need room around the equipment. Taken together, those two points mean that HVAC units can’t be crammed into the least amount of space possible.

The good news is that many new HVAC systems are designed for ease of maintenance. That will make it far easier for facility executives who want to ensure that the new HVAC system will operate at the lowest possible life cycle cost.


HVAC , design and construction , first costs , operating costs , energy efficiency

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