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Monthly Archives: February 2017

  • A Checklist for Heat Load Calculations

    To have an HVAC (heating, ventilation and air conditioning) system run at optimal efficiency, homeowners and business owners need to know the heat load of the building. This metric, measured in tonnage, determines which size of HVAC system to purchase. Selecting the right size system is important for efficiency. For example, over-sized systems don't properly de-humidify the air during the summer. Under-sized systems may not be able to effectively heat or cool a building. Homeowners and business owners want the right size to have efficient heating and cooling.

    The most common way to determine the heat load of a building is a Manual J calculation. A licensed HVAC contractor can complete this calculation for a fee. However, there are some online Manual J calculators that allow home and business owners to complete their own calculations. The key piece is not the calculation, however, but the inputs. Owners must know many details about the building in order to complete a Manual J calculation. The checklist below contains the inputs required to do a Manual J heat load calculation.

    Materials for Walls, Ceiling and Floors

    A heat load calculation takes into account the insulation properties of the house. For this reason, it's not enough to know that a home is “brick.” Homes with brick walls also may or may not have insulation. The insulation can be various types. The same principle applies to ceilings and floors. A building plan or an HVAC contractor may be required to find out this information.

    Window Type

    The insulating properties of windows can also vary, depending on whether the window is single or double paned. Even the frame type (usually metal, wood or vinyl) has an impact on the heat load calculation.

    Door Type

    Surprisingly, there are differences in insulation properties between wood doors. In fact, there are multiple types of wooden doors in the heat load calculation. The insulation depends on whether the door is hollow or solid. Metal doors also have drastically different heat properties.

    Ceiling and Window Height

    The ceiling height helps to determine how much air needs to be warmed or cooled. Window height also has an impact on the heat load calculation.

    Length x Width x Height of Walls, Windows and Doors

    This information helps determine the size of the home or business and how much air needs to flow through the building for proper heating and cooling.

    Orientation of the Building

    The orientation of the front door and windows can be north, south, east or west. Southern exposure tends to be warmer in the northern hemisphere, since the sun hits that surface year-round.

    With this checklist, home and business owners can begin to complete a heat load calculation. There are online resources available to assist. However, it's important to note whether the calculation assumes the house is a “block” or it asks for the inputs for “room-by-room.” Block calculations are simpler to complete, but they don't tell owners how much heating and cooling is required for each room. To properly size ductwork and maximize efficiency, a room-by-room heat load calculation is preferred.

  • Use a Heat Pump for Air Conditioning and Heating

    One way to think of a heat pump is as a reversible air conditioner, which means that one device can provide both heating and cooling. Heat pumps capture heat from the outdoors and compress it. The compressed heated air is then pumped around the home or business. The heat pump doesn't actually generate heat. The principle by which heat pumps work is the same as air conditioners. However, air conditioners cycle the opposite way, expelling heat to the outdoors, instead of drawing it in. While heat pumps are typically reversible and can function as air conditioners, not all air conditioners can be reversed to function as heat pumps.

    Although heat pumps have the advantage of both cooling and heating, their functionality is limited to a moderate climate. An example of an appropriate climate for a heat pump only system would be Washington, DC. As an air conditioner, a heat pump can provide cooling air during hot temperatures. When temperatures drop below freezing though, it becomes harder for a heat pump to work as a heater. Since it functions by drawing heat from the air, it struggles to draw heat from freezing air. One solution is to add electric resistance coils to the heat pump. These coils function as a furnace and provide heat when it's too cold to draw warmth from outdoor air.

    Above freezing temperatures, heat pumps can be up to 40% more efficient than gas furnaces. Heating air requires a great deal of energy. Gas furnaces physically heat the air with a flame. However, heat pumps transition the warmth outdoors into the indoors (though compressing the air can be energy intensive). Heat pumps are more efficient than furnaces until additional electrical resistance coils need to be used to heat the air, which usually occurs around freezing temperature. At this point, the electrical or gas resistance coils are not as efficient as a gas furnace.

    If a heat pump promises to meet your heating and cooling needs, there are a few options to consider. Heat pumps come in a variety of sizes, measured in tonnage. To properly size a heat pump, home and business owners should complete a heat load calculation. This calculation takes insulation, square footage and climate factors into account and then recommends a tonnage. Heat pumps are usually electric, but some resistance coils can be gas-powered, depending on your preferences. SEER, or seasonal energy efficiency rating, is another way to determine the best heat pump for a home or business. Higher ratings translate to a more efficient heat pump. With these options in mind, it's easy to select the appropriate heat pump for your home or business.

  • Do I need an air handler?

    Sometimes the number of components that make up an HVAC (heat, ventilation and air conditioning) system can seem overwhelming. Part of the reason is that HVAC systems are extremely flexible. You can pick only the components you need to heat and cool your business or home as efficiently as possible. In some cases, this involves buying an air handler.

    An air handler has a simple task, to take in air and send it around the home or business. Air handlers often include blowers, heating and cooling systems and filters. It handles much of the “ventilation” port of the HVAC system. Air handlers are commonly used in conjunction with air conditioners. The evaporator coil in the air handler can remove additional heat before sending the air throughout the house.

    Am I in the right climate for an air handler?

    An electric split system for air conditioning in a warm climate, like Florida, will benefit from an air handler. Working in tandem with the air conditioner, the air handler keeps the air cold and blowing.

    However, air handlers can also be beneficial in slightly cooler climates. They can contain both heating and cooling elements. The cooling element would be the evaporator coil, which removes excess heat from the air. Heating elements, like electric heating strips, can also be included in an air handler. In this case, the air handler adds additional heat to the air before blowing it around the home or business.

    While beneficial in cooler climates, air handlers are not as commonly found in cold truly climates, like Minnesota. A gas or electric furnace is commonly used in place instead. Pairing a heat pump with an air handler is typically not sufficient to warm a home or business in a climate that repeatedly drops below zero. A gas or electric furnace is a more effective way to heat the location.

    How do I select an air handler?

    If you live in a warm climate, where the combination of an air handler and air conditioner or heat pump provides sufficient heating and cooling, it's time to look at air handlers. The first step is to do a load calculation, which determines how much heating or cooling is required for the home or business. A Manual J calculation is standard and the most accurate, but rules of thumb can also be applied. The resulting number is the tonnage size of the HVAC system that you ought to purchase for the best efficiency.

    The next item to evaluate is what type of refrigerant the air handler uses. The most common types are R-22 and R410-A. Newer HVAC systems typically use the R-410A refrigerant, which is generally accepted as the more environmentally friendly and efficient refrigerant.

    Air handlers can also be sold with heating elements. This may or may not be necessary in your climate. If your home does not already have heat pump, the heating elements may be a good choice to warm the air in your home when it gets a bit chillier. The heating elements can also work in tandem with a heat pump for greater efficiency. It depends on the system you select for your climate.

    If you need any help determining if your home or business would benefit from an air handler, you can check with an expert or call National Air Warehouse at (888) 997-5160 for assistance.

  • HVAC Sizing: Why do a load calculation?

    A whole new vocabulary greets those who want to purchase a new HVAC system. Instead of seeing the normal housing “square feet” metric, people are likely to see measurements in “tons.” These are not the same tons that semi-trucks are hauling on the freeway. It's a measurement of the cooling rate, and it's about equal to 12,000 Btu/hr. To properly size an HVAC system, the buyer needs to determine how the home or office building loses and maintains heat.

    Since HVAC may seem like a complicated new world, new HVAC buyers might be tempted to use a 'rule of thumb' to determine the size of their HVAC system. These “rules” can be as simple as holding up a cut-out to the home. The hole that the house fits within is labeled with a ton amount. Other people will recommend a certain number of tons per square foot. This method is slightly better because it takes into account the weather conditions for the local area. However, there are disadvantages to using a rule of thumb.

    Using a 'rule of thumb' is like going to the store and picking out a shirt in your size without trying it on. If you are usually a medium, it's a good bet that a medium shirt will fit you. But, in some stores, a medium can be too tight to fit around your chest or so loose that the shirtsleeves go down to your elbows. Without accounting for the unique contours of your body by trying it on, it's possible that you can buy the wrong size. An improperly sized HVAC system is like an ill-fitting shirt; it does the job, but it doesn't do it as well as it could. For example, an over-sized HVAC system doesn't de-humidify the air as efficiently during the summer.

    The secret to purchasing the right size of HVAC system is to take more factors into account. Like the unique contours of your body, your home or business has unique characteristics. For a building, the unique characteristics are the materials used for the construction. Are the walls made of brick or siding? What type of insulation was used? How many vents are in the floor? The doors are made of what type of material? These characteristics (and others, such as your location) are used in a Manual J load calculation, an industry standard method to determine the HVAC size for a home or office building.

    With the internet, it is possible to do a Manual J load calculation yourself. There are many sites dedicated to the task. However, they do assume that you have the basic information about the materials used in the construction of the building. Many homeowners don't know what type of siding or insulation they have (or where to find it). If you don't know what ceiling type you have in your home, it's probably worth asking a professional to complete a calculation (according to Manual J or another method). A trained technician can quickly assess the location.

    An HVAC is a long-term investment, often heating and cooling a location for decades. Isn't it worth it to get the right size for maximum efficiency?

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