Kaiyi HVAC Manual Guide (EN)

IMPROVING THE BUILT ENVIRONMENT Last update: 8-31-2010 Designing Forced-Air HVAC Systems Heating and cooling design loads should be calculated for the home using the protocols set forth in the latest edition of the Air Conditioning Contractors of America’s (ACCA) Manual J (currently the 8th edition), ASHRAE 2009 Handbook of Fundamentals, or an equivalent computation procedure. ACCA provides free speed-sheets for performing Manual J calculations on their website ( http://www.acca.org/speedsheet/ ), though you will need their Manual J handbook to complete the forms. There are several software packages available that are designed to do Manual J load calculations, including (but not limited to):

Wrightsoft’s Right-Suite: http://www.wrightsoft.com Elite Software’s RHVAC: http://www.elitesoft.com/web/hvacr/elite_rhvacw_info.html Nitek Software’s Load Wizard: http://www.niteksoftware.com/web2008/product2008.html Adtek’s AccuLoad: http://www.adteksoft.com/ Commercial load calculation tools are generally not appropriate for residential sizing. Major discrepancies between residential and commercial load calculations often occur in relation to: Ventilation Rates Infiltration Rates Occupancy Hours Lighting Other latent and sensible internal gains Before hiring any HVAC contractor, you should require a minimum of Manual J and S calculations to be completed in your bid request.

If a contractor is either unfamiliar or unwilling to do these calculations, you are better off looking elsewhere for a contractor, regardless of how low that contractor’s bid may be. If a contractor is not willing to design your system based on the best available methods in the industry, what makes you believe that they are knowledgeable enough to provide you a quality installation? Excessive capacity, low airflow, high duct leakage, and improper refrigerant charge can easily lead to your system running at 70% efficiency or worse, so choosing a qualified contractor is very important.

It is also recommended to have your HVAC contractor agree to provide their services in compliance with ACCA's Quality Installation Specification ( https://www.acca.org/Files/?id=116 ). This is an ANSI-approved standard that describes precisely the steps a contractor must take to ensure a quality HVAC installation. Energy Efficiency vs Comfort? There will always be those in the HVAC industry that believe right-sizing is actually under-sizing or that it is an energy efficiency measure that disregards comfort. Building America’s goal has always been to minimize energy consumption while maintaining or improving comfort and durability.

SWA has right-sized numerous projects in which we have followed up with short and long-term monitoring to ensure that comfort is maintained within the home. When incorporated into a whole-building systems approach to home construction, right-sizing is an effective method. This is not to say that issues can not arise when right-sizing a home’s HVAC equipment. To be clear, HVAC design is just that…”design” at the onset of the project. Right-sizing only works if Consortium for Advanced Residential Buildings Steven Winter Associates, Inc. www.carb-swa.co m 50 Washington St. 6th F l, Norwalk , CT 068 54 tel 203-857-0200 fax 203-857-0200 307 7th Ave. Ste.

1701, New York, NY 10001 tel 212-564-5800 fax 212-741-8673 1112 16th St., NW Ste. 240, Washington, DC 20036 tel 202-628-6100 fax 202-393-5043

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quality control is maintained throughout the construction process. If the home is significantly leakier or building specifications change drastically from design, the HVAC design needs to be modified as well. In the majority of cases, it is not that your system was under-sized, it is that your home was poorly constructed. Design Conditions For programs such as EPA’s ENERGY STAR Qualified Homes and USGBC’s LEED for Homes, the outdoor cooling design temperature used for load calculations must be the 1.0% design temperatures as defined in the ASHRAE Handbook of Fundamentals for the nearest appropriate weather site. Indoor design temperature should be 75°F for cooling.

The infiltration rate should be assumed to be “tight” or equivalent. These programs have no specific requirements for heating as there isn’t the same concern about addressing both sensible and latent loads. It has been suggested that a 99% outdoor design temperature and 70°F indoor design temperature should be utilized for these programs. SWA typically uses the 0.4% (cooling) and 99.6% (heating) outdoor design conditions when designing projects outside of these national certification programs as a compromise between national programs and HVAC contractors (who typically utilize the mean extreme outdoor design conditions).

If your HVAC contractor actually does an approved load calculation method, they still likely utilize the mean extreme outdoor design condition. Many contractors also design for an indoor temperature of 70°F for cooling. This is not necessary, but contractors do it as they believe that providing a larger capacity system will reduce the number of callbacks. They would be better off actually sealing ductwork, so that the distribution system doesn’t leak. Typical forced-air systems leak an average of 15-30% of the supplied forced air (as SWA has commonly tested in new construction). What does a 1%/0.4%/mean extreme or 99%/99.6%/mean extreme outdoor design conditions mean?

This is the dry-bulb temperature that corresponds to annual cumulative frequency of occurrence. This value represents the value that is exceeded on average by the indicated percentage of the total number of hours in a year (8760 hrs). For example, the 0.4% outdoor cooling design temperature for Sterling, VA is 93°F. This means that the outdoor conditions only exceed 93°F on average for 35 hours per year, or 0.4% of the year. Just because a system is designed to this lower than mean extreme outdoor condition, it doesn’t mean that the system simply won’t be able to cool a home for 35 hours each year.

A properly sized system may only be able to cool to 76°F or 77°F rather than 75°F for these hours. The benefits (better dehumidification and lower energy consumption) of a right-sized system out weigh any slight temperature increase and those 35 hours are not consecutive. They are spread out during the peak of summer days or winter nights. A room that is 77°F, but is controlling humidity levels will feel more comfortable than a room that is 75°F but not effectively controlling humidity. EPA was working on the following draft disclaimer for requiring right-sizing for all Energy Star Homes. Though it never became official, it provides a good explanation for why to right-size:

“As part of your new home’s ENERGY STAR certification, engineered sizing calculations have been performed to match the cooling system capacity with the load requirements of your home. This helps ensure that your cooling system runs more continuously rather than in a short-cycling mode with frequent on-off operation. EPA has added this requirement to ENERGY STAR Qualified Homes for several important reasons. First, your equipment can operate much more Consortium for Advanced Residential Buildings Steven Winter Associates, Inc. www.carb-swa.co m 50 Washington St. 6th F l, Norwalk , CT 068 54 tel 203-857-0200 fax 203-857-0200 307 7th Ave. Ste.

1701, New York, NY 10001 tel 212-564-5800 fax 212-741-8673 1112 16th St., NW Ste. 240, Washington, DC 20036 tel 202-628-6100 fax 202-393-5043

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efficiently, much like a car getting higher fuel efficiency at highway speeds than stop-and-go traffic. This can also extend the lifetime of your equipment because on-off cycling imposes much more stress on critical components. Lastly, continuous operation also helps improve the comfort of your home because the cooling coils stay cold for a longer period of operation time, and therefore, can remove more moisture from the air. Right-sizing of your air conditioning equipment was based on national standard procedures developed by the Air Conditioning Contractors of America (ACCA) or equivalent computation procedure.

These calculations are based on recommended set-points for indoor comfort and predominant weather conditions assuming appropriate equipment selection and proper system installation. It should be noted that extreme weather conditions can always occur that may leave your air conditioning system with temporary limits on delivering full comfort performance. This is much like selecting siding, roofing and window materials to handle very harsh weather conditions, but not extreme weather such as hurricanes and tornadoes.” Common Design Assumption Errors Often a HVAC designer will size based on a maximum entertaining occupancy load expected in the home.

ACCA’s occupancy load guideline (Manual J 8th Edition: Section 22-3) is to design for the total number of full time occupants. If unknown, this should be based on two people for the master bedroom and one for each additional bedroom. For heating dominate climates, leave in occupants in the bedrooms. For cooling dominate climates, these occupants should be distributed throughout the living space, as they will typically be in these areas during the maximum load period.

When a builder/homeowner requests a system that can accommodate a large number of guests, this temporary occupant load needs to be handled by a supplemental cooling system or by a system that can shift capacity from zone-to-zone (a variable volume/refrigerant system). In addition, HVAC designers often include an internal lighting load. This is not a recommended practice unless there is minimal window area. The inclusion of lighting will minimize the design heating load and will inflate the design cooling load. Typically, homes will have few lights on during the peak summer hours, as daylighting will be utilized for the most part.

For lighting, equipment, and appliance load assumptions, ACCA’s Table 6 can be utilized. Equipment Sizing Heating and cooling equipment should be sized according to ACCA Manual S based on the loads calculated per Manual J protocols. Additional safety factors shouldn’t be applied when sizing a system. When sizing cooling equipment, it is important to ensure that both the sensible and latent capacities meet the required building loads, and not just the total cooling capacity is met. If slightly short on either sensible or latent capacity, the designer should first account for fan speed adjustments to meet capacity requirements prior to upsizing.

Energy Star only allows a maximum oversizing limit for air conditioners and heat pumps of 15% (except in Climate zones 5-8, which are allowed a maximum of 25% oversizing for heat pumps). As manufacturer’s equipment sizes typically come in half or one ton increments, it is acceptable to install the next available manufacturer’s size though it may exceed EPA’s oversizing limit. For example, if the design building load is 19,000 Btuh, a 2 ton air conditioner can be installed even though it is a ~21% oversizing. The designer/contractor should provide documentation of both the selected unit and the unit one size smaller for approval of this exception.

Consortium for Advanced Residential Buildings Steven Winter Associates, Inc. www.carb-swa.co m 50 Washington St. 6th F l, Norwalk , CT 068 54 tel 203-857-0200 fax 203-857-0200 307 7th Ave. Ste. 1701, New York, NY 10001 tel 212-564-5800 fax 212-741-8673 1112 16th St., NW Ste. 240, Washington, DC 20036 tel 202-628-6100 fax 202-393-5043

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In addition, indoor and outdoor coils should be matched in accordance with AHRI standards. SWA recommends obtaining the AHRI certification documents for each system installed from your HVAC contractor ( http://www.ahridirectory.org/ahriDirectory/pages/home.aspx ) and to verify that model numbers on the condenser, evaporator coil, and air handler/furnace match the documentation provided. For dual-capacity cooling equipment, when matching cooling capacity to cooling load, the total/full capacity of the unit should be referenced (not part load capacities).

Only in cases when there is a combined heating and cooling system and when the cooling load is substantially smaller than the heating load should an absolute sizing limit not be strictly enforced. This exception is provided to ensure that adequate heating is maintained within the home. It is the responsibility of the designer to ensure that the system will still provide adequate humidity control (enhanced controls, whole-house dehumidifier, etc.). If there is a need to accommodate a significant number of temporary occupants (guests) on a regular or sporadic basis, a supplemental cooling system (i.e., mini-split unit) or a variable volume zoning system should be utilized.

Supplemental & Auxiliary Heat Sizing (Electric Resistance Coils) For heat pump heating system, you will need some amount of supplemental heat provided by the resistance coils (or other back-up heating source) when the outdoor temperature is below the balance point of the heat pump, it is recommended that the resistant coils are staged. The capacity of the supplemental heating coils will need to be equal to the difference between the Manual J heating load and the high-speed output of the heat pump when the outdoor temperature is equal to the winter design temperature.

Request a balance-point diagram from the manufacturer on the unit selected to determine the capacity of the system at the desired outdoor design temperature. The maximum amount of electric resistance heat that is controlled by the second stage of the room thermostat should as closely sized to the supplemental heat requirement that is associated with the balance point diagram. An example of sizing the supplemental heat requirement: Assume the outdoor design condition is 17°F, cooling load of 19,105 Btuh, and a heating load of 21,947 Btuh.

The selected two ton heat pump provides 22,600 Btuh of heating capacity at 47°F and 14,000 Btuh capacity at 17°F (from AHRI rating), the equivalent resistance coil to meet the supplemental load of the heat pump is 2.52 kW: (22,600 Btuh – 14,000 Btuh) / 3,412 Btuh/kW = 2.52 kW This example uses a 17°F outdoor design condition, because it is available in the AHRI rating…but this example would need to be revised based on the balance-point diagram for the selected unit and the desired outdoor design condition. In terms of emergency heat (assuming the compressor fails), the total resistance coil sizing for the example two ton unit would be 6.62 kW (= 22,600 / 3,412).

Electric resistance coils typically come in sizes of 5, 8, 10, 15, and 20 kW. Two 5 kW coils that are staged would cover this unit. If smaller electric coil sizes were available, they should be utilized. Consortium for Advanced Residential Buildings Steven Winter Associates, Inc. www.carb-swa.co m 50 Washington St. 6th F l, Norwalk , CT 068 54 tel 203-857-0200 fax 203-857-0200 307 7th Ave. Ste. 1701, New York, NY 10001 tel 212-564-5800 fax 212-741-8673 1112 16th St., NW Ste. 240, Washington, DC 20036 tel 202-628-6100 fax 202-393-5043

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