Module 7 - HVAC Sysytems.pptx

Strand RESNET Rater Training – HVAC Systems © 2023 STRAND Dallas I Texas 972 620 8204 HVAC What does HVAC stand for? Despite the name, HVAC doesn’t have anything to do with vacuuming. It actually stands for the three different functions provided by the system. They are: •Heating •Ventilation •A...

Strand RESNET Rater Training – HVAC Systems © 2023 STRAND Dallas I Texas 972 620 8204 HVAC What does HVAC stand for? Despite the name, HVAC doesn’t have anything to do with vacuuming. It actually stands for the three different functions provided by the system. They are: •Heating •Ventilation •Air Conditioning © 2023 STRAND Dallas I Texas 972 620 8204 How Does an HVAC System Cool and Heat My Home? Some HVAC systems cool with a unit called a condenser. Others cool with a device called a heat pump. They both function similarly in that they grab warm air from inside your home and move it outside. This is actually what lowers the indoor temperature. Air conditioning does not literally blow cool air inside—it takes the warmer air away. The main difference between a heat pump and a condenser is that a heat pump is also involved in the act of heating your home - when you want to warm up the air inside your home a heat pump works in reverse, pulling warmer air from outside and moving it indoors. A condenser does the cooling only, meaning if you have one you’ll need to rely on your furnace alone for heating. © 2023 STRAND Dallas I Texas 972 620 8204 © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Central Air Conditioner A central air conditioning unit uses a split system that regulates air through ducts installed in your home. It is also known as a ducted system. The split aspect implies that the system is a combination of two main units. The outdoor unit packs in the condenser and compressor. While the indoor unit comprises the evaporator coils & air handler © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Ductless Mini-Split Such type of an air conditioner is a combination of an outdoor unit comprising of a compressor & a condenser that comes along with one or more indoor units. These indoor units are mounted on a wall and equipped with air blowers. The indoor & outdoor units are connected through tubing and refrigerant circulates through them in variation depending on the type of usage. © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Floor Mounted Air Conditioner Floor mounted air conditioners are designed for convenience if you prefer a mini-split but lack the required space for a wall mounted unit. The indoor unit of floor-mounted AC rests on the floor, and the outer unit can be installed without major site preparation or any ductwork. This arrangement is also ideal for spaces with tilted walls such as attics or building constructed by fragile materials such as glass. © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Smart Air Conditioner Smart air conditioners are a type of mini-split, window or portable air conditioner that are IoT enabled. These ACs are connected to the Wi-Fi and come with a native app providing global control through a smartphone © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Geothermal Air Conditioning System Geothermal heating & cooling is considered a relatively new method, it works by utilizing the insulating properties of the earth. Since the temperatures under 4 to 6 feet of land remain consistent all year regardless of the weather, geothermal technology takes advantage of this to heat & cool your home more efficiently. © 2023 STRAND Dallas I Texas 972 620 8204 Types Of Air Conditioners Hybrid / Dual Fuel Air Conditioner A hybrid system is one that combines a gas furnace with an electric air-source heat pump to deliver a cost-effective & efficient performance in terms of heating & cooling. Depending on the temperature outdoors, the system automatically switches between burning fossil fuels and the usage of electricity. You program the temperature at which the system switches from heat pump to furnace or you can make the manual switch too. During the summer season, the heat pump works as it is functioned to, pulling hot air from inside your home and throwing it outdoors. During the winters, this process is reversed and heat is distributed throughout your home. When the temperature is too cold for a heat pump to function efficiently, the furnace kicks in. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating Furnace Furnaces are one of the most common types of heating systems in the United States. A forced-air furnace heats the home by burning fuel—natural gas, propane, oil, or electricity—to heat a metal heat exchanger. The heat transfers to the surrounding air, and a fan blows the heated air throughout the home via ducts and vents. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating Boiler Traditional boilers, radiators, and baseboard heaters are radiant or hydronic heating systems. They heat water in a central boiler using natural gas, propane, fuel oil, or electricity. The heated water or steam goes through a network of pipes to radiators or baseboard heaters throughout the house. When the water within the radiator heats up, the air heats up through a process called convection. The hot air circulates through the room by displacing cold air. When heat leaves the water, it returns to the boiler again. This continues until your home reaches the desired temperature. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating Heat Pump There are three main heat pump types: air-to-air, water source, and geothermal. Heat pumps use electricity and refrigerant to collect heat from the air, water, or ground (depending on the type) and deliver it to your home. Heat pumps work in reverse in summer by transferring the home’s heat out. In cold months, the heat pump collects air from outdoors and blows or pumps it over a heat exchange surface, causing a refrigerant liquid to evaporate. This gas moves to a compressor, which increases the pressure and causes its temperature to rise. The heated gas is then passed over the internal heat exchanger’s surface. A fan pushes heat either directly into the room from the indoor unit or through the ductwork to warm the house. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating In-Floor Radiant Heating In-floor radiant heating systems—both electric and hydronic—use thermal radiation and electromagnetic waves to heat your home. Electric wires or water-filled tubes are installed underneath the flooring and warm a room by directly heating the floor instead of the air. Hydronic in-floor heating uses a boiler system and a variety of fuel sources, such as natural gas, oil, wood, solar, or some type of combination. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating Active Solar Heating Active solar heating uses solar energy to heat liquid or air, then transfers solar heat directly inside the home or to storage for later use. If solar energy isn’t enough to heat the home, a backup home heating system provides additional help. Liquid systems are often used when there’s a solar heating storage system. However, both liquid and air active solar heating systems can supplement forced-air systems. © 2023 STRAND Dallas I Texas 972 620 8204 Home Heating Hybrid Heating A hybrid heating system combines an electric heat pump with a gas-powered furnace. This combination maximizes energy savings and system performance. The heat pump heats the home when outdoor temperatures are moderate. You can program your thermostat to automatically switch over to the gas furnace when temperatures drop below 40 degrees Fahrenheit. © 2023 STRAND Dallas I Texas 972 620 8204 Air Exchangers This is a mainstay of the ventilation portion of your HVAC system. The air exchanger’s job is to “exchange” stale air for fresh air. This allows the air inside your home to stay cleaner than it would otherwise. It may also help reduce allergens and control humidity. Evaporator Coils and Coolant AC units and heat pumps contain many important parts. AC units made for the past decade or so use a coolant called Puron instead of Freon. Older units do use Freon. It is also important to note that as of January 2020, Freon is no longer made in or imported to the United States. © 2023 STRAND Dallas I Texas 972 620 8204 © 2023 STRAND Dallas I Texas 972 620 8204 Vents/Registers and Ductwork Without vents and ductwork your HVAC system would be pointless. Ducts carry the air to various places around the home, and vents/registers provide an opening for the air so it can heat or cool the room in question. Many types of ducting systems exist, and some are not compatible with certain AC units or heat pumps (especially in older homes) so if you plan to invest in a new HVAC System you definitely should check into duct compatibility first. © 2023 STRAND Dallas I Texas 972 620 8204 © 2023 STRAND Dallas I Texas 972 620 8204 A Thermostat A thermostat allows you to adjust and control the temperature of your home. You’ll need to make sure that the thermostat you are using is actually compatible with that system (many manufacturers sell compatible thermostats for this reason). Consider your choice between a smart thermostat, a digital thermostat and an oldschool analog thermostat. © 2023 STRAND Dallas I Texas 972 620 8204 Water Heaters What’s the Difference Between High Efficiency (EF) Ratings vs the New Uniform Energy Factor (UEF)? Ever researched water heaters before a purchase, then you’ve probably compared high efficiency, mid-efficiency and standard efficiency information. To help consumers in their water heater purchase decisions, the Department of Energy has developed new industry standards. Due to inconsistent, unreliable interpretations of High Efficiency (EF) ratings across national brands, all water heating manufactururers are now required to comply with the new DOE testing procedures and rating standards. Beginning, June 12, 2017, EF ratings will be replaced with the new industry standard for measuring energy efficiency in water heaters called, Uniform Energy Factor (UEF). The new UEF rating method improves the industry’s ability to: Define consistent standards for measuring energy efficiency performance Simplify the water heater selection process More accurately reflect real-world scenarios that impact energy efficiency ratings © 2023 STRAND Dallas I Texas 972 620 8204 Water Heaters © 2023 STRAND Dallas I Texas 972 620 8204 Water Heaters © 2023 STRAND Dallas I Texas 972 620 8204 Water Heaters © 2023 STRAND Dallas I Texas 972 620 8204 Conventional storage water heaters. These traditional tanks, which range from 20 – 80 gallons, keep hot water at the ready. When you turn on your hot water faucet, water flows from the top of the tank through the pipes to the faucet. Cold water then flows into the bottom of the tank, where it is warmed. Because water is always kept warm, even when not being used, this type of water heater can waste energy through standby heat loss. Tankless/demand water heaters. Unlike conventional water heaters, tankless ones operate on demand. When you turn on the tap for hot water, cold water is heated with a gas burner or with electric elements as it passes through the water heater. With this system, you only get the hot water as needed so it saves energy and money. However, it can initially be more expensive than the more economical conventional heater and it can fail to heat water quickly enough when demand is high. © 2023 STRAND Dallas I Texas 972 620 8204 Tankless coil and indirect water heaters Similar to a tankless or demand water heater, a tankless coil heats water on demand as it flows through a heating coil in the main furnace. With no standby heat loss, this system is efficient in cold months when the heating system is used regularly, but can be inefficient when used in milder climates, where the furnace isn’t needed frequently. An indirect heater can be a more efficient choice because it uses a storage tank that allows the furnace to turn on and off less often. Solar water heating systems. These systems are 50% more efficient than gas or electric water heaters and include storage tanks and solar collectors. They can be used in any climate and the solar power is free. Like the tankless heaters, solar heating systems have a higher initial cost and may need a backup system for cloudy days. Heat pump. These pumps use electricity to move heat from one point to another and can be two to three times more efficient than conventional electrical water heaters. However, these pumps can only be used in locations withDallas milder climates ranging from 40° to 90°. © 2023 STRAND I Texas 972 620 8204 NATE Certification NATE certification stands for the North American Technician Excellence, the largest nonprofit independent certification organization in the United States for heating, ventilation, air conditioning and refrigeration technicians. It is a nationally recognized organization that offers optional certifications developed and supported by industry professionals. NATE certification establishes a level of professionalism and highquality standards, making it easier for consumers to make informed decisions when choosing technicians and companies to install, maintain or repair heating and cooling equipment in their homes or businesses. You can earn both installation and service certification, specialize in oil, gas or other heating and cooling areas and gain senior level technician status through various NATE certification tests. © 2023 STRAND Dallas I Texas 972 620 8204 Airflow Dynamics – HVAC Verifier © 2023 STRAND Dallas I Texas 972 620 8204 Basics of Comfort Comfort is highly individual and is a function of the surrounding air temperature, the relative humidity of the space, the temperatures of the surrounding surfaces (mean radiant temperature or MRT), the airflow rate which affects the evaporative cooling rate from our skin, and the amount of clothing we wear. All of these work together to produce “comfort” and we all have different requirements for each of the different factors. Is it any wonder that comfort is a huge issue for both builders and homeowners? The comfort zone is the space within a room that is 2’ from the perimeter walls and 6’ from the floor. It is the air temperature, relative humidity, surface temperatures surrounding that space and air velocity within that space that we are mostly concerned with. People lose and gain heat primarily through convection, evaporation and radiation. © 2023 STRAND Dallas I Texas 972 620 8204 Surrounding Air Temperatures The temperature of the air in a space is affected by the rate of heat transfer through the surfaces surrounding it, amount of heat energy produced by items within the space (people, pets, appliances), and the temperature and velocity of conditioned air supplied to that space. Load calculations are performed for heating and cooling seasons in order to determine how much conditioning energy (heating or cooling) needs to be supplied to a space to keep the air temperature at a certain level © 2023 STRAND Dallas I Texas 972 620 8204 Default Indoor Design Values The default design indoor temperature for the heating season is 70°F and the air within the comfort zone should be within + 2°F of the thermostat setting, giving a 4°F range between conditioned spaces. The default design indoor temperature for the cooling season is 75°F; the air within the comfort zone should be within + 3°F of the thermostat for a single zone (giving a 6°F range between spaces) and within + 2°F for a multi-zone design. © 2023 STRAND Dallas I Texas 972 620 8204 © 2023 STRAND Relative Humidity Relative humidity (RH) is the percentage of moisture held by the air in relation to the amount of moisture the air could hold if it were totally saturated. Dew point temperature is the temperature at which the water vapor in the air changes into liquid. This process is called condensation and occurs on surfaces that are cooler than the surrounding air. Dew point temperatures can be found by reading the psychometric chart. It is a more reliable indicator of how comfortable the air is than relative humidity. Relative humidity can also be determined by reading the psychometric chart and is not a reliable indicator of comfort since it is temperature dependent. When the temperature goes up, the RH goes down because the warmer air has a greater capacity to hold moisture (of course, this doesn’t account for any Dallas I Texas additional moisture) 972 620 8204 Basics of Energy & Pressure Thermodynamics The first law of thermodynamics states that the total energy in the universe is constant and cannot be created nor destroyed, but is transferred by heating, cooling or mechanical work. The second law of thermodynamics states that systems in contact with each other that have differences tend to balance. Air, heat, and water move from areas of high concentration to areas of less concentration (high pressure to low pressure, hot to cold, wet to dry). Air has sensible (temperature) and latent heat (moisture). © 2023 STRAND Dallas I Texas 972 620 8204 Heat Energy There are three types of heat energy transfer: conductive, convective, and radiant. Conductive heat flow is the flow of heat through a solid or from solid objects that are touching each other. Convective heat flow is the flow of heat through a liquid or gas (like air). Radiant heat flow is the flow of heat from a hot surface to a cooler surface. As long as the surfaces can “see” one another, heat will be transferred. Just as pressure differences direct the movement of air, temperature differences direct the movement of heat. Nature is constantly trying to maintain a balance and always takes the path of least resistance to achieve that balance © 2023 STRAND Dallas I Texas 972 620 8204 Conductive heat transfer is the transfer of heat through a solid or between solids that are touching each other. Conduction is the heat transferred through the building assembly (floor, walls, ceiling) and insulation is used to slow it down. Examples of conductive heat transfer are heat loss/gain through the ceiling, through the walls, through the floor, through the windows and doors (all the building components that make up the building envelope). © 2023 STRAND Dallas I Texas 972 620 8204 Radiant heat transfer is heat transfer between a warm surface and a cooler surface and doesn’t require air movement or the two surfaces to touch. Solar radiation (heat energy radiated from the sun) happens in a perfect vacuum (space) every morning when the sun comes up and warms our side of the planet. Far-infrared radiation occurs in homes, usually in two locations: attics and windows © 2023 STRAND Dallas I Texas 972 620 8204 Measuring Energy A British thermal unit (Btu) is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit at sea level when the water is 39.2º F. While the United States uses British thermal units to measure the quantity of energy, most other countries use the term joule. One Btu (about the amount of heat produced by burning a kitchen match) is equal to 1,055 joules, named after James Prescott Joule, an English brewery manager and amateur physicist whose discoveries in the mid-1800’s led to the 1st Law of Thermodynamics. A joule is the amount of work needed to produce one watt for one second (a watt-second). © 2023 STRAND Dallas I Texas 972 620 8204 Pressure Compression and expansion of gas affect temperature, volume, and the buoyancy of the gas. Archimedes (287 BC - 212 BC) discovered the buoyancy principle while trying to find out if a goldsmith had committed fraud. By measuring the displacement of water and weight of an object and comparing it to the displaced water level and equal weight of pure gold, he was able to determine that fraud had occurred. Buoyancy is the upward force on an object. Normal Stack Effect is the effect of hot air rising within a home that is surrounded by cooler air. Reverse Stack Effect is the effect of cool air falling within a home that is surrounded by warmer air © 2023 STRAND Dallas I Texas 972 620 8204 Daniel Bernoulli (1700-1782) described the drop in air pressure above a hole when the velocity of the air blowing across the hole goes up (Bernoulli Effect). Bernoulli noted in 1738 that gas particles move and when they collide with something, they apply pressure. When they move (kinetic energy) through a larger volume, the particles travel more and collide less (decreasing pressure as volume increases). When they move through a smaller volume (compression), they travel less and collide more (increasing pressure as volume decreases), just as described by Boyle’s Law. © 2023 STRAND Dallas I Texas 972 620 8204 The combined gas law states that the ratio between the pressure-volume product and the temperature of a system remain constant. R represents the constant. It is a combination of Boyle’s Law, Charles’ Law, and GayLussac’s Law. By using a mechanical system of compressing and expanding a gas, the temperature of the gas changes as it changes phase (liquid to vapor, vapor to liquid). In the refrigerant cycle shown here, a compressor changes the cool low-pressure vapor into a hot high-pressure vapor through work. As the condenser fan blows outside air over the coils containing the gas, it changes form to a subcooled high-pressure liquid. As it passes through the metering device, it expands (dropping temperature and pressure) into a cold low-pressure liquid. As the warm house air is blown across the coils containing the liquid, the heat from the house air is absorbed into the refrigerant changing it into cool lowpressure vapor. © 2023 STRAND Dallas I Texas 972 620 8204 Pressure differences are measured in positive or negative Pascals with respect to (w.r.t.) the other zone. For example, a home could be + 2 Pa w.r.t. the outside, or the attic could be -3 Pa w.r.t. the house. In order to determine the direction of the air leakage, it is critical to measure a pressure differences w.r.t. the different pressure zones. © 2023 STRAND Dallas I Texas 972 620 8204 Supply leaks cause the house to undergo a negative pressure change, while return leaks cause the house to undergo a positive pressure change. • 2.5 ton system moving 1,000 cfm: 1,000 cfm pulled into the return grille, 200 cfm leaks out of the supply side, 800 cfm pushed into the house. Pulling 1,000 out and putting 800 back in = negative pressure. • 2.5 ton system moving 1,000 cfm: 800 cfm pulled into the return grille because 200 cfm is being pulled from return leaks in unconditioned basement, 1,000 cfm being pushed into the house. Pulling 800 out and putting 1,000 back in = positive pressure. © 2023 STRAND Dallas I Texas 972 620 8204 How Loads are Calculated Heating loads are calculated by using the Heat Transfer Multiplier (HTM) formula over the course of the heating season for the climate where the house is built. The building envelope surfaces (the foundation walls, floor systems, exterior walls, windows, doors, attic kneewalls, and ceilings) are all sources of heat loss to the outside. Additionally, there is air infiltration and exfiltration plus intentional ventilation that must be accounted for as well as duct losses. Ducts conduct some heat through the insulation (R-6 or R-8) but lose more through leaking hot air to unconditioned spaces, or pulling in cold air from these unconditioned spaces. The internal loads of people, lights, and appliances also generate heat and help offset some of the heat loss through the envelope and systems. Internal loads increase the cooling load calculations, but decrease the heating load calculations. © 2023 STRAND Dallas I Texas 972 620 8204 Cooling loads are calculated by using the HTM formula over the course of the cooling season for the climate where the house is built. Certain building envelope surfaces (exterior walls, windows, doors, attic kneewalls, and ceilings) are all sources of heat gain from the outside. Additionally, there is air infiltration and exfiltration that must be accounted for as well as duct gains. Ducts gain some heat through the insulation (R-6 or R-8), but gain more through leaks that pull in hot air from unconditioned spaces. The internal loads of people, lights, and appliances also generate heat that must be removed by the mechanical equipment. © 2023 STRAND Dallas I Texas 972 620 8204 Ventilation loads are created when we bring outside air in for the occupants. It is not created by the exhaust ventilation from kitchen range hoods and bathroom exhaust fans. Do not calculate those intermittent devices as part of the ventilation load of the home. The ventilation load is calculated by multiplying the number of occupants by 7.5 cubic feet minute (cfm) and adding 1 cfm per 100 ft2 of conditioned space (ASHRAE 62.2). © 2023 STRAND Dallas I Texas 972 620 8204 The moisture load is calculated in grains. One pound of water vapor is equal to 7,000 grains at 70°F and sea level. One pound of dry air (at the same conditions) takes up 13.33 cubic feet (1 cubic foot weighs 0.075 pounds). The psychrometric chart shows the thermodynamic properties of moist air and can be used to determine the relative humidity, dew point, drybulb temperature, wet-bulb temperature, specific volume, humidity ratio, and enthalpy (Btu/lb of dry air). Manual J Table 1A lists the design conditions for a number of locations and includes psychrometric information in addition to indoor and outdoor design temperature data © 2023 STRAND Dallas I Texas 972 620 8204 Outdoor Design Conditions The winter outdoor design temperature is a temperature that the air is warmer than 99% of the time during the three coldest months. ACCA’s Manual J is the industry source for outdoor design conditions. Heating Degree Days (HDD) are the total number degrees colder than 65°F (Base 65) during the heating season. For example, if the average daily temperature is 55°F, then 65 - 55 = 10 heating degree days. The summer outdoor design temperature is typically a temperature that the outside air is hotter than only 1% of the time during the three hottest months. Cooling degree days (CDD) are the total number of degrees that the outside temperature is warmer than 65°F (Base 65). © 2023 STRAND Dallas I Texas 972 620 8204 Indoor Design Conditions The indoor design conditions are the temperature and humidity levels that we want to maintain over the course of the heating and cooling seasons. We use an indoor design temperature of 70°F for the heating season and an indoor relative humidity level between 20% and 30%. We use an indoor design temperature of 75°F for the cooling season and an indoor relative humidity level between 25% and 50%. An indoor temperature of 75°F with a RH level at 40% will give us a dew point of 49°F. Any surfaces cooler than that will result in condensation. An indoor temperature of 70°F with a RH level at 25% will give us a dew point temperature of 32°F, resulting in condensation (frost) occurring on any surfaces cooler than the indoor dew point. Dew point can be determined with a psychrometric chart and the grains of moisture in the air. © 2023 STRAND Dallas I Texas 972 620 8204 Ductwork Ductwork installed in a conventional attic can drop the efficiency of the system by 50%. When that ductwork is installed in a semi-conditioned buffer zone (unconditioned basements inside the building envelope, interfloor spaces), the efficiency ranges between 50-100% of the system. © 2023 STRAND Dallas I Texas 972 620 8204 Air Infiltration Air leakage through the building envelope accounts for about 1/3 of the heating and cooling loads on a home. Internal Loads Internal loads are generated by people, pets, plants and appliances. People give off heat (some of us are regular furnaces) and moisture that needs to be accounted for. Duct Design First, try to get the ductwork inside the building envelope. This reduces the duct leakage to the outside (which has an energy penalty) and generally improves performance © 2023 STRAND Dallas I Texas 972 620 8204 Distribution Geometry Duct systems usually take the shape of a trunk and branch, perimeter loop, spider system, or radial system. Trunk and branch systems are the best type to be installed if the architecture and construction materials support it, using sheet metal trunks and flexible duct branches. The trunk and branch system can have a trunk that is one size (extended plenum), a trunk that reduces in size over its length (reducing plenum) or multiple trunks (primary-secondary trunk). The air handler should be centrally located on the trunk; however, it is possible to have it off-set and still get the performance needed. It simply requires more work because there are large differences between the effective lengths of the ducts at the air handler and end of the trunk. © 2023 STRAND Dallas I Texas 972 620 8204 Flexible Ducts Pre-fabricated flex duct took the craftsmanship away from duct design and installation and replaced it with a Dadaistic art form. Now, it can be left to the installer to interpret where the duct should go, what size should be used, while rejecting standards in favor of chance and randomness. Sheet Metal Ducts Sheet metal ductwork has a lower friction loss rate than the other types of ducts. The reducing plenum system addresses that issue by equalizing the fitting losses of the branch take-offs, helping to move air into the ducts closer to the air handler. The reduction should take place when the velocity in the trunk drops to about ½ the velocity of the first part of the trunk. Velocity is calculated by dividing the air flow rate (cfm) by the cross-sectional area of the duct in square feet © 2023 STRAND Dallas I Texas 972 620 8204 Efficiency Ratings Each type of equipment has a different efficiency rating category. • AFUE: Fuel output in Btu’s per hour / fuel input in Btu’s per hour • HSPF: Average annual Btu’s of heating / annual average watt-hours of electricity used • COP: Total heating capacity in Btu’s per hour / (total electrical input in watts x 3.412). This is a steady state efficiency rating. • SEER: Average annual Btu’s of cooling / annual average watt-hours of electricity used • EER: Total cooling capacity in Btu’s per hour / total electrical input in watts (btuh/watt) © 2023 STRAND Dallas I Texas 972 620 8204 Furnaces Furnaces heat the air through the combustion of fuel. They have an electric motor driven fan that moves the air through the distribution system (ductwork), pulling cool air from the house and pushing the heated air back into the home. While the minimum efficiency rating of furnaces is currently 78% AFUE, they are typically found with either an efficiency rating of 80% AFUE or a 90% + AFUE. Efficiency ratings for furnaces can be obtained from AHRI © 2023 STRAND Dallas I Texas 972 620 8204 Over sizing furnaces does not make the home more comfortable. It only takes about 20 minutes to route all the air in a typical home through the furnace (if everything is designed and installed correctly). Over sizing the furnace by 100% may cut that time in half, but the sense of comfort will be restored with a right sized piece of equipment in the same amount of time. We reach our comfort level in about ½ the time it takes to reheat the thermal mass of the home, well before the furnace has completed its cycle. Unlike air conditioning systems, oversizing furnaces does not have an impact on their steady state efficiency. © 2023 STRAND Dallas I Texas 972 620 8204 Blower When a heating only system is installed, the system pressures are lower because there is no indoor coil for the supply air to pass through. The amount of air flowing across the heat exchanger has a direct effect on the temperature rise (creating the temperature difference between supply air and room air). Heat Exchanger The heat exchanger is the device that transfers the heat from burning the fuel to the air stream. Manufacturers typically have a range of temperature rise that the heat exchanger can perform; outside of that range, bad things can happen. © 2023 STRAND Dallas I Texas 972 620 8204 Air Conditioners Air conditioners work using the concepts of refrigeration. Refrigeration is taking heat from a place you don’t want it and placing it in a place you do want it. In our case, we don’t want the heat in the home and we do want the heat outside. Air conditioners have four basic components: a compressor, an expansion valve, and two heat exchanger coils (evaporator and condenser). By changing the pressure and temperature of the refrigerant, we can use it to move the sensible and latent heat from inside the home to outdoors. Sensible heat is heat that is added or removed that changes the temperature, but not the state (solid, liquid, and vapor). Latent heat is heat added or removed that causes a change in state (solid, liquid, vapor), but not a change in temperature. © 2023 STRAND Dallas I Texas 972 620 8204 The saturation state is when a refrigerant is both liquid and vapor; the liquid and vapor have the same temperature. This occurs when a refrigerant is undergoing a phase change and when it has reached equilibrium. Superheat is the amount of heat contained in a vaporized refrigerant above the saturation point (or boiling point). If superheat doesn’t exist within the refrigerant cycle, the refrigerant can enter the compressor in liquid form and potentially tear the compressor Subcoolingup. is the temperature removed from the vaporized refrigerant when it is condensed back into a liquid. Because a TXV device keeps superheat at a constant level across a wide range of operating conditions, measuring superheat on a system with a TXV is completely inaccurate. © 2023 STRAND Dallas I Texas 972 620 8204 The compression ratio has an effect on energy efficiency and superheat. Higher compression ratios reduce the efficiency of the unit. The metering device takes high temperature, high pressure liquid refrigerant from the condenser and sends a low temperature, low pressure saturated refrigerant (liquid and vapor) to the evaporator. The evaporator coil is a refrigerant-based heat exchanger. It takes low temperature, low pressure saturated refrigerant and vaporizes it into a low temperature, low pressure vapor The condensing coil is another heat exchanger within the system. It takes the high temperature, high pressure vaporized refrigerant and condenses it to a medium temperature, high pressure liquid. It does this in three steps: de-superheating, condensing, and subcooling © 2023 STRAND Dallas I Texas 972 620 8204 Air Source Heat Pumps Heat pumps work by moving heat instead of converting it from a fuel (electricity or gas). It is essentially a two-way air conditioner that heats by reversing the refrigerant flow, causing the heat to be transported from the outside to the home. Geothermal Heat Pumps Geothermal heat pumps use the earth instead of the air. The earth has a fairly constant temperature all year long, while the air temperature fluctuates seasonally. This constant temperature provides greater efficiency for heating and cooling when using a heat pump. © 2023 STRAND Dallas I Texas 972 620 8204 There are two main types of geothermal heat pump systems. The open loop system (Ground Water Heat Pump, Surface Water Heat Pump) pulls groundwater from a well or body of water and uses it instead of the water antifreeze solution through the underground piping. This water is then discharged to either the surface of the ground, another well, or back into the pond or lake. There are a couple of serious challenges with this system; the water tends to be corrosive due to the hydrogen sulfide content and shortens the life span of the heat exchangers (there are valid concerns over introducing contaminants into the water supply). If the water is hard (more than 100 ppm) or if you know it contains hydrogen sulfide, don’t even consider an open loop system. The closed loop system (Ground Coupled Heat Pump, Surface Water Heat Pump) uses the waterantifreeze solution (which is environmentally safe) or a refrigerant as described above. © 2023 STRAND Dallas I Texas 972 620 8204 © 2023 STRAND There are different ways of configuring the underground loops as well. The loops can be in vertical bores or in horizontal trenches. Additionally, the loops in horizontal trenches can take a spiral form which shortens the length of the trench needed Pressures Pressures can be measured with a manometer. Manometers can measure the static and velocity pressures within a duct system, the stack effect in multi-story buildings, and gas pressures in combustion exhaust systems (flue pipes). Velocity pressure is the difference between stagnation (or total pressure) and the static pressure. The manometer can be used with a velocity pressure pitot tube to measure the velocity pressure, which can be converted to velocity in feet per minute using the ACCA Duct Slide Rule’s auxiliary calculations. The ACCA Duct Wheel app is a digital version of the Duct Slide Rule. Dallas I Texas 972 620 8204 The total external static pressure is key to determining if the duct system is correctly sized. If the air handler manufacturer includes the filter in their product performance data (read the footnotes!), the external static pressure is measured in the return plenum (pre-filter) and supply plenum (ignore the + or - signs and add the two together to get the total). If the manufacturer does not include the filter, or if a cased coil is installed, the external static pressure is measured across the coil in the air handler cabinet. Furnace external static pressure is measured in the return plenum (pre-filter) and in the transition between the furnace and the cooling coil. If the furnace manufacturer does not include the filter in their performance data, simply remove the installed filter. © 2023 STRAND Dallas I Texas 972 620 8204 Temperature If the temperature rise across the heat exchanger is too low based on the manufacturer’s specification, it indicates there is too much air moving across the heat exchanger. Airflow temperatures should be measured in the return plenum within 12” of the air handler (entering air temperature) and in the supply plenum within 42” of the air handler, but out of line-of-sight of the heat exchanger (leaving air temperature). This provides the temperature rise (or drop). A digital thermometer with a 15” probe seems to work the best. If it is colder than 50℉ outside, do not check the temperatures in cooling mode © 2023 STRAND Dallas I Texas 972 620 8204