4 FM quick reads on HVAC
1. Why Some Geothermal Systems Will Save More Than Others
Geothermal heat pump systems promise to provide lower cost heating and cooling than conventional systems, with far less reliance on fossil fuels. But the amount of savings varies from system to system. To understand why, there are a couple of points facility executives should keep in mind.
One important point to remember is that geothermal systems offer more savings in cooling-dominated climates. But if the load between heating and cooling is balanced, geothermal systems can also operate cost effectively.
Another important point: The greater the temperature difference between the air and the ground, the more efficient the system.
A final efficiency consideration: With large systems, very warm ground temperatures — for example, on a hot day in late summer — may make it necessary to dissipate some heat in a fountain or other open water source or to use it for domestic purposes.
2. Fans May Offer Surprising Energy Savings
It’s no secret that HVAC systems account for a significant percentage of the energy used by a building. But it’s not only the heating and cooling systems that present opportunities for big savings.
Facility executives should also take a close look at the fan systems in a building. In doing so, however, facility executives should understand how the energy consumption of a fan varies with its speed.
The amount of power used by a fan is proportional to the cube of the speed of the fan. That’s counterintuitive. Chillers, for example, use less energy to produce a ton of cooling at full load than at part load. Fans are just the opposite. At full speed, they are at their least efficient. That means even a small reduction in fan speed can produce surprising energy savings.
One option for cutting fan speeds is to install variable frequency drives on fan motors. That way, fans can be slowed down when conditions in the building don’t require them to operate at full speed.
3. When Selecting HVAC Products, Look at Part Load Performance
I'm Ed Sullivan, editor of Building Operating Management magazine. Today's topic is the importance of the part-load performance of HVAC systems.
HVAC systems are designed to handle extreme conditions. Components of the system are sized for the hottest and coldest days of the year. On those days, the chiller or boiler is running at full load and at maximum efficiency.
But for the rest of the year, the system is running at part load. And in the past that has meant a sharp drop off in energy efficiency.
Today, that needn't be the case. Variable frequency drives, for example, can bring significant improvements in the part load performance of chillers. On the heating side, consider modulating boilers to achieve the same goal.
When you're evaluating HVAC equipment, determine how often your system will be running under part-load conditions. And if that will be a frequent occurrence, look for a system that will be efficient at the part-load conditions that it will actually be facing.
4. HVAC, Lighting: Symbiotic Relationship
Hello. This is Greg Zimmerman, managing editor of Building Operating Management magazine. Today’s topic is energy efficiency as it relates to lighting and HVAC systems. Facilities should be designed so that HVAC and lighting energy use can both be minimized simultaneously. The two are related in that the more artificial lighting that is used, the more energy will be required to cool the air heated by those lamps and ballasts. Of course, the lighting itself uses energy, too, so the fewer artificial lights that are on, the more energy efficient the building. Increase the amount of natural light in a building and use efficient lamps to cut lighting energy. Use sensors to dim or turn off lamps when natural light is abundant. Make sure that daylighting strategies are considered when sizing HVAC equipment so that equipment is not oversized and inefficient.