Building envelope design is a specialized area of engineering and architectural design that centers on indoor climate control. A building envelope includes all the elements of the outer shell of a building that separates the conditioned (indoor) environment from the unconditioned (outdoor).
A well-performing building envelope controls rain, air, heat, and vapor on the inside of a building. In addition, it must support the building to resist and transfer dynamic loads of the structure, and its finish should meet the aesthetics desired both inside and outside.
Rain and vapor control is the job largely performed by the roof and walls; heat flow control rests mainly with the ceiling, and air control includes the roof, walls, doors, windows, ceiling, and even the foundation of a building.
The effectiveness of a building envelope can be measured by its ability to protect against weather and climate, the level of indoor air quality it maintains, its durability, and its energy efficiency. To achieve these objectives, building envelopes ideally need to have a solid structure, an air barrier, a vapor barrier, a thermal barrier, and a drainage plane.
Heat pumps transfer heat from a source to what is known as a heat sink. Heat naturally flows from warmer spaces to cooler places. However, a heat pump can make that flow work in reverse, too. Air conditioners and freezers are familiar examples of heat pumps in action; the term “heat pump” covers a broad range of devices in general and can be applied to many HVAC components used for cooling and heating. These devices are also often used with hot water heaters in domestic applications.
A heat pump can use a basic cycle for air conditioners and refrigerators in addition to water heaters, too – the flow of heat is just reversed when used for heating applications. While electrical resistance heaters used to be more popular than they are today, they have been gradually replaced with heat pumps, which offer significant improvements in energy efficiency.
Heat pumps require evaporators and condensers in order to perform. The pumps use a refrigerant to help absorb heat where it vaporizes – in the evaporator – then they release that heat where the refrigerant condenses – in the condenser. Insulated pipes allow the refrigerant to travel, producing efficient thermal energy transfer across various distances.
Most new homes today have HVAC systems that are too large for the structures they serve. In order to correctly determine HVAC load calculations, time and attention to detail are required. Many contractors rely on rules of thumb to determine the sizes of the systems they install; it’s usually based on the square footage of the conditioned floor area. They often use 400 to 600 square feet per ton as the rule.
Every house is unique. Consider this: The same house rotated 90 degrees could result in a different cooling load by 25% or more!
Bigger is not always better – especially with heating and cooling systems. Oversized cooling systems, for example, can create a clammy house because they don’t run long enough to dehumidify the air, they have shorter lifespans because they turn on and off so often, and they are more expensive to run and to install. It should be noted that the Energy Star New Homes program requires systems that are no more than 15% oversized for residences.
HVAC Load Calculations
The right way to size an A/C unit is with Manual J, a protocol developed by the ACCA (Air Conditioning Contractors of America). This method, which was once done by engineers with pen, paper, and slide rules, is now almost always done with computer programs. Other contractors using 500 square feet per ton are often installing an air conditioner that is 2, 3, or even 5 times larger than it should be. The techs at A-1 Guaranteed Heating & Air, Inc acknowledge that most newer homes, even in hot climates, have loads of 800 square feet per ton or more. Cooler climates and/or well designed high-performance homes can be as high as 1500, 2000 even 2500 square feet per ton.
At A-1 Guaranteed we use Right-Suite Universal by Wrightsoft. Contact us if you’d like more information about how we can help you with your HVAC project.
Room by Room Airflow
Room air distribution defines the way air is introduced to, flows through, and is removed from areas. It can usually be defined as one of two types: dilution (or mixing) and displacement.
Dilution (Mixing) Systems
These systems blend supplied air with room air to produce air at the desired temperature and humidity. In cooling mode, cool supplied air is usually about 55 degrees F and exits an outlet at high velocity, caused by diffusers. The high velocity causes turbulence, causing room air to mix with supply air. Since the entire room is almost fully mixed, variations in temperature are small. Usually, air outlets and inlets are located in the ceiling.
These systems supply air directly to occupied areas at low velocities for minimal mixing. Displacement systems are ideal for ventilation and cooling of large areas and high spaces where energy can be saved if only the occupied zone below is treated.
Displacement room airflow uses the difference in air density between an upper zone and lower zone to stabilize the temperature and humidity of the air. Convection creates vertical air motion into the upper zone to not only move heated air higher, but also to move contaminants up and away from occupants in the lower zone. Since supplied air is moved directly into occupied space, the air temperature of the supplied air must remain higher than that in mixing systems – usually above 63 degrees F.
Insulation represents the first line of defense for your home against unwanted hot and cold air infiltration. Adding insulation is an effective way to increase your home’s energy efficiency. This not only includes adding insulation to your attic, but also sealing air leaks around electrical boxes, door frames, recessed lights, plumbing, and more. Air leaks can account for up to 30% of a home’s energy loss. When it comes to adding insulation to the attic, the way to go today is to blow in loose-fill insulation.
You’ll want to focus on two tasks when it comes to attic insulation: increasing the amount and sealing air leaks in the ceiling. The payback for upgrading attic insulation and sealing air leaks can be as short as three years. Radiant-reflective insulation is popular for homes these days because it makes the attic dust-free for storage, keeps blown-in insulation from blocking rafter bays, and reduces the radiant heat gain from the roof.
Although blown-in loose-fill insulation is not as commonly used as batt insulation, it can be installed quickly and will completely cover the ceiling. Loose fill can also be blown in over any existing insulation. Interested in reading more on the topic? Click here to read our blog.
Why Check Static Pressure?
Checking the static pressure of a residential HVAC system is crucial; since the entire point of a system is to move air (warm or cool) around a home, measuring the pressure gives an indication of how well the system is performing.
Static pressure is the pressure of airflow anytime air is moving in any direction within a duct system. It can also be thought of as the resistance to airflow in an HVAC system’s ductwork and components.
Did you know that many home performance issues can be detected by infrared technology? An infrared camera can diagnose problems like missing insulation, thermal bridges, moisture intrusion, and air leaks. The technology has been used for more than 40 years – and is a valuable diagnostic tool because it doesn’t require damaging any walls, ceilings, or other structures of the home.
Tools that use this technology include infrared cameras (IR cameras), thermal imaging devices, and thermographic scanners. A professional who uses the device is a thermographer, and the image produced by IR cameras is called a thermogram.
Many people think that these devices measure surface temperatures of buildings; however, this is incorrect. What they measure is the intensity of infrared energy, otherwise known as radiant energy, that is being emitted by the surface at which it is aimed.
During a home energy audit, one of the tests that may be performed is a blower door test. This survey determines the degree to which a home is airtight. Why should homeowners establish good air tightness for their homes?
An airtight home helps avoid moisture condensation issues.
Air leaks in a non-airtight home reduce energy efficiency, increasing energy consumption.
Airtight homes prevent uncomfortable drafts caused by air leaks.
Establishing proper air tightness helps determine the amount of mechanical ventilation that will be needed to provide good indoor air quality.
A blower door is a fan that mounts into the frame of an exterior door. This powerful fan pulls air out of a home, which lowers the indoor air pressure. Higher-pressure outdoor air flows through any unsealed openings and cracks, which can be detected by an auditor using a smoke pencil or gauges.
There are two types of blower doors: calibrated and uncalibrated. Calibrated blowers should always be used by auditors because it has several gauges that measure the amount of air that the fan pulls out of the house. In contrast, an uncalibrated blower can only locate leaks, not measure them.
A-1 Guaranteed is the leader in heating and cooling repair and maintenance, water heater service and repair, home energy audits, new window installation, and HVAC and solar services in California. We serve all of Contra Costa, Napa, and Solano counties.
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