Going for the Gold in HVAC
In that theme, Verle A. Williams, P.E., C.E.M., C.S.D.P., president, Utility Services Unlimited Inc., discussed how to harvest the gold in your chiller plant.
It’s important to keep it simple, said Williams. A well-designed control system is mandatory. Minimize manual operation, and develop a clear operating procedure and backup failure mode.
Do a due diligence review, he said. “It’s a lot easier to make a change when it’s a pencil and eraser.”
In performing a feasibility study, determine:
• Can the existing equipment meet the needs?
• Is the type of system optimum?
• Will the system fit the site?
• Are water treatment and balancing considered?
• Do savings calculations account for recurring preventive maintenance costs?
• Is the design energy efficient?
• Are all control valves two-way?
• Is there multiple sized equipment for light load operation?
“Attack the energy hogs wherever they are,” Williams said. Dirty coils equal poor performance. “Let’s take care of those coils,” he urged. Get rid of costly safety factors, such as oversized pumps. Avoid a piping maze. Also, he noted, bad location for flow sensors provides worthless results.
CHILLER RETROFIT CONSIDERATIONSJon Haviland, P.E., C.E.M., C.L.E.P, assistant vice president, Marx Okubo Associates, addressed chiller plant retrofit considerations. “Don’t simply replace,” said Haviland. “Spend a little extra time now to maximize the system.”
Don’t overestimate the building load and oversize the equipment to handle the overestimated load, he warned.
Reasons for retrofit, he said, include age, efficiency of the equipment, facility changes, and refrigerant update. Options to consider are hybrid plants, primary-secondary chiller water distribution, variable-flow primary, chiller sizing, and condenser water system.
Both the engineer and contractor should have experience in this type of retrofit project, Haviland said. And they need to familiarize themselves with the existing plant.
“Constructability needs to be considered in the design phase,” he said. “Coordination is critical during the construction phase.”
SAVING HOT WATERSaving energy in hot-water systems was the subject talked about by Gary Hogsett, P.E., C.E.M., energy management specialist, Burns & McDonnell. To save energy, Hogsett said, you can recommend a low-flow aerator. Commercial kitchens use tons of hot water, he noted. A standard pre-rinse spray valve uses 6 to 9 gpm. Going to low flow will take that down to 0.5 gpm.
The biggest source of heat loss in a gas water heater is the flue, he stated. Therefore, when installing a new water heater, a model having a flue damper should be specified in commercial applications.
“A problem with older water heaters is scale,” Hogsett said. And the water heater’s temperature setting can increase the amount of scale. The higher the temperature, the larger the amount of scale. A water heater set at 140°F will have significantly less scale than one set at 180°.
An intelligent water heater controller can be used to raise and lower the temperature to meet periods of peak and low demand, he said. This can save a lot of energy.
Tankless water heaters “are getting better and better,” said Hogsett. These units eliminate the tank and provide hot water on demand. With electric models the savings are not as great, he remarked.
Insulation of piping is another way to save energy. “Insulation is such a cheap fix,” he said.
A direct-fired water heater can achieve 99-plus percent combustion efficiency. Heat pump water heaters are also highly efficient, Hogsett said. In addition, you can recover heat from a chiller to heat water.
COST-EFFECTIVE HVACSteve Tom, Ph.D., P.E., director of technical information, Automated Logic Corp., then tackled the subject of cost-effective HVAC, which he said is “providing a comfortable and healthful environment for the least possible cost.” But, he emphasized, you still want to maintain the productivity of people.
How much does HVAC affect the efficiency and productivity of people? Tom said a Cornell University study on the effects of indoor air temperature on keyboard data entry found that, if you raised the temperature from 68° to 77°, the data entry rate went up by 150 percent while errors dropped by 44 percent.
A Helsinki University study found the peak temperature for productivity to be 72° to 75°. The study reported a 1.1 percent decrease above 75°. A UCLA study found that air conditioning had the biggest impact on student learning. And in an experiment at Portland High School, students scored highest on a test when room temperature was 72°.
How do we quantify the indoor environment? We have, said Tom, “the dreaded C word: comfort.” You can label it environmental index or IAQ, he said, but “whatever you call it, you need to stay in the comfort zone.”
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has an entire chapter on comfort, commented Tom, encompassing temperature, humidity, and other factors.
Tom explained that work on developing a comfort index has been done by Bill Gnerre and Kevin Fuller. They went through ASHRAE research relating comfort to humidity and condensed it into a temperature vs. humidity table. They then converted this table to a comfort index. A numeric score on the index shows how well an HVAC system is performing.
What if you don’t measure humidity or other characteristics like CO2? You can “let occupants adjust the set point,” said Tom. The bottom line is to “develop a metric that works for you.”
Energy is important, concluded Tom, but “people are more important and more expensive. A cost-effective HVAC program can save energy and make people more productive.”
Publication date: 11/12/2007