ARCHIVED - HVAC

Heating, ventilating and air conditioning (HVAC) account for some of your highest energy expenses, but these systems are also critical to your guests' comfort and satisfaction. If your facility is too cold or too hot, you can expect complaints. HVAC systems also contribute to your facility's air quality, and fresh air is particularly important in enclosed or high-odour areas. For optimum efficiency, ensure that the functions of each HVAC component complement the others   especially when ventilation systems help distribute warm and cold air.

There are many types of HVAC systems, but the majority of hotels and restaurants in Canada use self-contained, packaged systems that combine heating, ventilating and air conditioning. Rooftop HVAC units (RTUs) are often used in single-zone, single-storey buildings, such as restaurants. Incremental HVAC units or packaged terminal air conditioners (PTACs) enable discrete control in each suite and are commonly mounted to outside-facing walls or below windows in guest rooms of small to mid-size hotels and motels. Fan coil units are a component of central systems used in mid-sized and larger hotel facilities. In these systems, air is blown over coils that have been heated by boilers or cooled by chillers in a central plant. Savings can also be realized with the efficient use of cooling towers, air-to-air heat exchangers, air-handling units (AHUs), heat pumps and other HVAC components.

Common HVAC Measures

• Pick the right system when replacing your HVAC unit, usually at the end of its life cycle. In addition to energy efficiency, the size, weight, maintenance costs and noise levels are important considerations.

• Outdoor air economizers should be included with air-handling units, so outdoor air can be used for free cooling during spring and fall or on cool summer nights when the humidity level is not too high.

• Smart thermostats provide preset limits for heating and cooling   overriding unnecessarily high or low settings by guests or staff. These thermostats also feature digital controls and readouts that ensure greater accuracy than the sliding levers on traditional units.

• Night temperature setbacks involve the installation of an automatic thermostat that controls the temperature when a restaurant, for example, is closed.

• Heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) have balanced exhaust and supply fans that meet all ventilation needs without creating drafts and air-pressure imbalances. HRVs can feature efficiencies as high as 85 to 95 percent, with payback in roughly 3.5 years. Consider these units whenever air is continuously exhausted and make-up or ventilation air is required.

• Variable-speed drives (VSDs), described in the Motors and Drives section, can be used with variable-air-volume (VAV) systems to adjust fan speeds according to operating requirements at different times of the day. In kitchens, for example, fans can be linked to burners to reduce energy consumption during off-peak cooking periods. Be careful, however, not to cut exhaust to the point that kitchen odours permeate other areas of your facility.

• Zone isolation and demand control ventilation (DCV) reduce airflow when low carbon-dioxide levels indicate a room is not in use. Implementing these measures may involve the use of variable-frequency drives (see the Motors and Drives section) and shut-off dampers, as well as reductions in the amount of outside air used by your HVAC system. Energy is saved not only because air distribution is reduced, but also because less air must be heated or cooled.

• Removable and re-usable insulation for pipes, valves and fittings is made of non-combustible materials and can provide paybacks as short as four months. Traditional insulation is often not replaced once it has been removed or damaged during maintenance. This can lead to tremendous heat loss or gain, as well as condensation and safety hazards. Removable and re-usable insulation provides a solution by simplifying both maintenance access and thermal-barrier replacement.

• Proper maintenance is critical to any system, since it helps reduce operating costs, extends operating life and avoids costly repairs. This is especially true with cooling towers, which are subject to scale deposits, clogged nozzles, biological growth, poor airflow and poor pump performance. These factors can diminish performance and raise operating costs by 10 to 25 percent. For air-handling units, buying high-quality filters will reduce air-borne dust and contaminants. In new boilers, proper maintenance can deliver savings of up to 20 percent. Look for more maintenance information in the Energy Tips section of this guide.

Heating-Specific Measures

• High-efficiency condensing boilers will save you a great deal of energy when it is time to replace old boilers. These units can achieve seasonal efficiencies as high as 96 percent (compared with 75 percent for old boilers). Incremental paybacks of two to six years are common compared with purchasing midrange replacement boilers, but initial costs can be twice as high. For example, the piping distribution and terminal-heating units may need to be redesigned for condensing boilers.

• Boiler flue gas economizers are heat exchangers that preheat water using boiler-stack and exhaust gases. With installed costs of approximately $35,000, economizers deliver a 5 to 10 percent increase in efficiency and, in large facilities, paybacks of four to 10 years.

• Air preheaters use hot stack gas to preheat fuel and air prior to combustion. These units cost approximately $15,000 and have paybacks in 2.5 to 3.5 years.

• Boiler combustion and oxygen-trim systems minimize energy loss by reducing the amount of excess air or fuel in a boiler stack. An automated oxygen-trim control system ensures the proper fuel-to-air mixture is maintained. With a typical cost of $10,000 for a 300-horsepower boiler, these units deliver energy reductions of 1 to 5 percent and paybacks of approximately five years.

• Boiler blowdown heat recovery uses a heat exchanger to extract thermal energy from hot water that is continuously drained from a boiler. Prices range from $10,000 to $35,000, depending on the amount of steam supplied. Paybacks are approximately 6.5 years.

• Continuous boiler blowdown monitoring and control systems reduce the amount of hot water continuously drained from boilers. These systems typically cost $2,500 to $6,000, with approximate paybacks of five years.

• Automatic vent dampers for boilers prevent residual heat from being drawn up the warm stacks, reduce the amount of air that passes through furnaces or boiler-heat exchangers and improve comfort conditions during the winter by helping retain humidity in a building.

Cooling-Specific Measures

• Energy-efficient chillers have better controls, condensers and compressors than regular units. Their costs, however, may not always yield reasonable paybacks and may not make up for inefficiencies in other parts of air-conditioning systems, such as pumps, cooling towers and controls.

• Refrigerants themselves can save you energy. For example, chillers that use an HCFC-123 refrigerant currently have the highest energy efficiencies, at 0.49 kW per ton.

• Thermal energy storage (TES) enables you to store cool water for later use as an air coolant. This function is particularly valuable for use at peak demand times during summer days. Approximate payback is 10 years.

The Vocabulary of HVAC

Btu/h, or British thermal units per hour, measure heat produced by boilers and cold produced by chillers. A single unit is the equivalent of 0.000295 kW or 0.000001055 GJ/h (one millionth of a gigajoule per hour).

Boiler hp (horsepower) measures boiler power and is equal to 33 520 Btu/h, 9.8 kW, 15.7 kg/h of steam or 0.0353636 GJ.

Boiler efficiency is calculated according to the formula: output energy divided by input energy multiplied by 100. Calculations are affected by factors such as thermal efficiency and fuel-to-steam efficiency.

Chiller efficiency measures power input per ton of cooling produced by larger chillers. A lower number indicates higher efficiency. The unit of measurement is kW/ton, in which ton is the amount of cooling produced when one imperial ton of ice melts. One ton equals 12 000 Btu/h or 3.516 thermal kW.

Energy efficiency ratio (EER) measures the performance of smaller chillers and rooftop units (as opposed to the kW/ton, which is used to measure the power of larger chillers). EER is calculated by dividing the cooling capacity in Btu/h by a chiller's power input in watts. The higher the EER, the more efficient the unit. Standard heat-pump units often have EER values of 8.9, where higher-efficiency units may reach 10.

Coefficient of performance (COP) is energy output divided by energy input. The higher the COP, the more efficient the chiller or heat pump.

Seasonal energy efficiency ratio (SEER) applies to rooftop units with cooling capacities less than five tons. SEER is a seasonally adjusted rating based on representative residential loads.