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By Stefan Domby
Energy Efficiency Article Use Policy
As important as the energy savings are, understanding the cost of that energy is equally important. At the end of the day it comes down to money saved over money spent. Energy recovery on a 100 percent outside air handling DX unit may have an impressive energy savings to the modeling engineer, but with the combined cost of a gas-fired AHU section and gas that costs less than a dollar/therm, the facility engineer who is paying the bill may have a differing opinion. On the other hand, if the energy wheel avoids a significant demand electric charge, the energy wheel may be the solution. Make sure you understand the utility rate structure for the building and any unique ratchets that may apply.
The energy savings based on the energy conservation measures (ECMs) that have been modeled can occur on a component level (such as motors, variable frequency drives, controls and lights) or they may reflect the replacement of an entire system (such as going from constant volume to variable air volume or from variable air volume to chilled beams).
The first cost for the ECMs must be well described and supplemented with diagrams and sketches so that a qualified cost estimator or contractor can provide the appropriate cost to the ECM for each alternative modeled. This step is not a trivial matter. Replacing a motor with a high efficiency motor or providing a new VFD are not things that can be looked up in a book; the installed cost must be understood. The price of an air-handling unit is one thing but providing a crane to lift that unit to the roof is a real cost. Of course not all installation issues are as dramatic; however, you must understand the basis of your comparison: is it the cost of the equipment or is it the installed cost of the equipment with labor?
No matter how great the destination, if the journey to get you there kills you, what does it matter? Such is the case with the difference between HVAC renovations in an unoccupied as opposed to an occupied building.
Think about it as a real life example: if you want to remodel your bathroom and you have to rent a hotel room for several months just to shower, you would probably just move out until the project is done. Or, if you have a good neighbor that will only charge you utilities and toilet paper costs, you'd utilize their bathroom.
Building owners are faced with similar dilemmas, but with a few more people to consider and much higher stakes. But, of course, any problem can be solved with the right amount of money. This where skilled cost estimators and contractors comes in. A detailed conversation should address swing space, moving costs, dust control, noise control, temperature control, temporary heat and AC, power outages, fire watches, etc. Replacing an HVAC system in a building takes a lot of money and developed phasing plans. A life-cycle cost report for the replacement of your HVAC system may not capture all the costs involved but it can give you an order of magnitude to help drive the discussion and decisions.
One thing is for certain, that hotel room is looking pretty good. Phasing the work in an occupied space can triple the cost of the project and can really ruin a life cycle cost evaluation, but many owners are faced with this very issue without the availability of a suitable swing space. So planning is everything. Plan to spend money, plan to work on premium hours, plan to phase the project so that whatever area is disrupted at night is returned to working condition the next day, and plan on an extended project schedule.
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