The ASHRAE guidelines are expressed as throw (T50) divided by characteristic length (L). The characteristic length is the distance from the outlet to the opposite wall or to the midpoint between adjacent outlets. Manufacturers' catalogs list outlet throw in feet by outlet size and CFM to three distances: 150, 100, and 50 fpm terminal velocity of the air jet leaving the device. To use the ASHRAE table recommendations, divide published throw in feet by characteristic length (also in feet).
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For example, a 12-in. x 15-in. office has a design supply air flow of 120 CFM. To use a 4&#;way blow, square perforated face diffuser in the center of the room, the throw to 50 fpm terminal velocity should be between 12 and 18 feet (2.1 x 6 and 3.2 x 6). A 2-way corner blow outlet in one corner of the room with throw between 25 and 38 feet (2.1 x 12, and 3.2 x 12) would also work.
Throw that is too short results in too much air in some parts of the room (drafts due to dumping) and not enough in others (stagnant areas). Throw that is too long result in drafts due to air jets bouncing off walls or colliding with adjacent air jets. Manufacturers' throw data are for isothermal jets. Throw from overhead devices changes by about 1% per degree F difference between room air and supply air temperature, decreasing for cooling and increasing for heating.
2) When selecting outlets, match the outlet shape and throw pattern to the shape of the room.
Long, narrow rooms can use one way blow outlets at one end of the room or 2-way blow outlets in the center. A 4-way blow square outlet in the center of the room selected for the short dimension would leave stagnant areas at the ends of the room. It might be possible to find a 4-way blow rectangular outlet that has appropriate throws in both the long and short dimensions. An imaginary dividing line across the width of a 2-x-1 room that creates 2 nearly square rooms could be served by two 4-way blow square outlets, one in the center of each square.
Especially in small rooms, the lighting designer and the sprinkler engineer often want to locate their systems and equipment in the center of the room. Choosing HVAC outlets that avoid the center of the room can ease coordination.
3) Noise is the other key parameter for selecting registers, grilles, and diffusers.
Generally speaking, the HVAC system should not be the loudest sound in the room. Return and exhaust inlets can be selected based on maximum face velocity. 250 fpm to 275 fpm is a good guideline for very quiet applications like residences, hotel rooms, and theaters. For process exhaust, noise is important, but function is more important. Therefore, select process exhaust inlets based on required capture velocity even if noise might result.
Select supply air outlets based on neck velocity and manufacturers' catalog NC ratings. Neck velocity under 500 fpm is often a good starting point for quiet selections.
Catalog NC ratings are for individual devices with ideal entry conditions and include a fixed room attenuation effect (usually 10 dB). Two devices in the same room will double the noise: a 3 dB increase; 4 devices means a 6 dB increase. Dampers, elbows, or squashed flex duct that create uneven airflow in the diffuser neck will also increase noise. If the actual room effect is less than 10 dB, the diffuser or grille will be louder than the catalog rating. Erring on the side of quieter selections allows for field conditions that increase unwanted noise.
4) Calculate carefully.
When calculating pressure drop for return or exhaust systems, remember to include 1 velocity head to accelerate still air in the room to duct velocity. Loss coefficients for hoods, grilles, and fittings are friction losses and do not include the energy to accelerate air to duct velocity.
5) Watch for short circuiting.
Return/exhaust air inlet location is more flexible than supply outlet location because throw or area of influence is not a factor, especially if face velocity is kept low for quiet operation. Figure 1 shows that the velocity near an exhaust inlet decays to less than 10% of the face velocity within 1 duct diameter of the inlet.
October 28,
When you&#;re ready to say goodbye to your old heating and cooling system, the Service Champions team is standing by to help you select a system personalized to your home. From factoring in coastal weather and climate to understanding efficiency ratings, we&#;ll help you make an informed decision when buying a new HVAC system.
HVAC collectively refers to a range of heating and cooling system types, each carrying certain advantages. The main types of HVACs include:
Furnaces: Available in gas, propane, and electric models, furnaces generate and distribute heat throughout the home via ductwork. Furnaces deliver powerful heating in a variety of climates but may be less efficient overall than other heating options.
Central air conditioner: Central ACs cool, filter, and redistribute air throughout your home using ductwork.
Heat pumps: During winter, a heat pump transfers extracted warm air rather than use fuel to heat it. These units also usually feature a reverse valve that switches to cooling mode as needed, offering high efficiency over other HVAC models in most weather conditions.
Mini-splits: Mini-split systems work similarly to heat pumps, but they feature air handlers in each room or &#;zone&#; that connect to a central outdoor condenser. They run quietly, offer high energy savings, and don&#;t require ductwork, making them ideal for smaller spaces.
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Consider these tips when buying a new HVAC system.
Climate plays an important role in the performance and efficiency of an HVAC system. For example, the Bay Area climate is characterized by dry summers and mild, wet winters with occasional cold snaps. Systems that perform well in these climates, such as heat pumps and mini-splits, may offer better efficiency and humidity control over others.
Proper HVAC sizing is essential for performance and longevity. Sizing refers to heating and cooling capacity, and the right capacity prevents issues related to oversized or undersized units, such as insufficient cooling or heating, uneven temperature, high energy bills, and extra wear. Heating capacity is measured in British Thermal Units (BTUs), and cooling in tons, with higher measurements corresponding to greater capacity.
Your home&#;s square footage provides a broad baseline for calculating its cooling and heating load. HVAC technicians also consider its layout, insulation, doors, windows, household occupancy, and other factors to precisely calculate cooling and heating needs.
Heating and cooling equipment accounts for about half of residential energy consumption. With California electricity rates among the highest in the country, it&#;s often worth investing in a high-efficiency system.
Modern HVAC equipment offers superior efficiency over older models. Various rating systems measure efficiency, but annual fuel utilization efficiency (AFUE) mainly measures furnaces while seasonal energy efficiency ratio (SEER) measures cooling equipment. Look for models with high ratings to reduce long-term energy and fuel consumption and utility costs.
In California, homeowners may be eligible for various tax rebates and incentives for energy-efficient HVAC installations. Under the Inflation Reduction Act, for instance, eligible homeowners can claim enough in rebates to significantly offset the cost of a heat pump installation.
Different HVAC systems and individual models vary in noise output. Most modern central ACs operate at 60 decibels or lower, about as loud as a regular conversation, while mini-splits run at about 20 to 30 decibels or on par with a whisper. Noise output doesn&#;t necessarily reflect the system&#;s quality, but some homeowners have stronger preferences for quiet operation.
If you&#;re replacing a forced-air system, verify the condition and compatibility of your ductwork with your preferred new unit before purchasing. Old or damaged ducts may need repairs, modifications, or replacement altogether to ensure efficiency. Weigh the costs of ductwork installation or repair against ductless HVAC configurations &#; in some cases, ductless systems may be more cost-effective.
New HVAC systems offer advanced features and capabilities that enhance comfort. Options include:
Zoned controls
Smart thermostats
Humidity and air quality controls
Following your HVAC installation, proper maintenance will keep it running smoothly. Many manufacturers require homeowners to arrange professional maintenance as per warranty terms to maintain compliance &#; in other words, neglecting warranty-required maintenance may leave you responsible for covering repair costs.
With Service Champions Maintenance Value Plan, customers get access to annual tune-ups, priority scheduling, and discounts on repairs. Annual inspection and maintenance doesn&#;t just ensure warranty compliance, but also helps prevent untimely repairs and optimizes your system&#;s performance.
A heating & cooling system only performs as well as its installation and maintenance allows it. With a knowledgeable HVAC contractor, you can trust in their abilities to assess your home and install your system according to permits and safety standards. Look for these key characteristics when hiring an HVAC contractor:
Satisfied customers: Check reviews for positive experiences &#; Service Champions has thousands of 5-star reviews from happy customers.
Transparency: Whether explaining the installation process or providing upfront pricing, a trustworthy provider should operate with transparency and good communication.
Professional development: Look for providers committed to ongoing training to stay ahead of the industry. With the Champions University, our certified HVAC technicians continually advance their expertise.
Serving neighborhoods throughout the Bay Area, Service Champions helps customers find the right heating and cooling system for their California home. Trust the local expertise of our team to guide you through choosing a new HVAC system with flexible financing &#; contact us or book online today.
The cost of a new HVAC system varies widely based on several factors, including system type and installation complexity. Warranty coverage, extra features, and other considerations may also influence costs. Schedule a consultation with Service Champions and one of our Comfort Advisors will assess your home&#;s needs, calculate an accurate estimate, and provide you with options unique to your situation.
The timeline for installing a new HVAC system ranges from one day to up to a week depending on the type of system, its scale, and other factors. For example, ductless mini-split installations may take as little as a day, not including assessment, while replacing a central AC and modifying ductwork may add significant time to the project.
Several signs suggest it&#;s time for HVAC replacement, such as increasingly frequent or costly repairs, high utility bills, insufficient heating or cooling, and poor indoor air quality.
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