A supply air duct delivers 1,200 CFM with a temperature rise of 20°F across a heating coil. Using the sensible heat formula Qs = 1.08 × CFM × ΔT, what is the sensible heat output?
Pre Installation Design
Question · Medium
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Short
A 5-ton air-conditioning system is operating at rated capacity. How many BTU per hour of heat does it remove from the conditioned space?
Question · Easy
An air handler supplies 2,000 CFM. The moisture removed from the air is 30 grains per pound of dry air. Using Ql = 0.68 × CFM × ΔW, what is the latent cooling capacity?
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Air enters a cooling coil at 1,500 CFM with an enthalpy of 31.5 BTU/lb and leaves at 23.0 BTU/lb. Using Qt = 4.5 × CFM × Δh, what is the total cooling load?
An air-conditioning system is oversized for the space it serves. Which operating problem is most likely to result?
Six feet: a hard-hat anthem
A 3-ton split air conditioner draws 3,000 watts while cooling at its rated capacity. What is its Energy Efficiency Ratio (EER)?
A room has a sensible cooling load of 18,000 BTU/hr. The supply air is 55°F and room design is 75°F. What airflow (CFM) is required to deliver this sensible cooling?
On a psychrometric chart, a condition has a dry-bulb temperature of 80°F and a wet-bulb temperature of 67°F. Which statement about this air state is correct?
Question · Hard
When designing a low-pressure residential duct system, the Trane Ductulator is most commonly used with which design method?
A ductulator is used at a friction rate of 0.08 in wc per 100 ft to size a supply run carrying 400 CFM. The ductulator indicates a 10-inch round duct. What is the approximate air velocity?
Ductwork Hvac Materials
A rectangular duct measures 24 inches by 8 inches. What is its cross-sectional area in square feet?
According to SMACNA and the HVAC Duct Construction Standards, what is the maximum recommended length for a flexible duct run between connections?
Which duct sealing class, per SMACNA and ASHRAE standards, requires all transverse joints, longitudinal seams, and duct wall penetrations to be sealed?
For a typical low-pressure galvanized sheet metal supply duct (duct width 24 in and pressure ±2 in wc), which minimum galvanized sheet metal gauge does SMACNA typically require?
For flexible duct installed in an accessible attic, what is the maximum support spacing allowed by SMACNA and the Fibrous Glass Duct Construction Standards?
A 90° elbow with a 10-inch diameter is in a duct system. The fitting table lists its equivalent length as 30 feet. If the actual run of straight duct is 60 feet, what is the total effective length used for sizing?
Air flows at 1,800 CFM through a rectangular duct with a cross-sectional area of 2.0 sq ft. What is the air velocity in feet per minute (fpm)?
When constructing fibrous glass ductwork to the Fibrous Glass Duct Construction Standards, what closure method is required at all transverse joints?
In a direct-expansion refrigeration system, what does the term "superheat" refer to?
Installation Refrigeration Hvac Systems
A refrigerant pressure-temperature chart shows R-410A condensing at 120°F, where the liquid line leaving the condenser measures 105°F. What is the subcooling?
Compared with R-22, how does R-410A affect refrigerant system pressures and components?
When evacuating a system for refrigerant charging, what is the industry-recommended target vacuum level (in microns) before breaking the vacuum with refrigerant?
When sizing a refrigerant suction line, the primary design goals are to:
Where should the sensing bulb of a thermostatic expansion valve (TXV) be mounted on the suction line?
On a TXV-fed system, raising the superheat adjustment (turning the stem counterclockwise) will produce which effect?
Refrigerant suction lines that pass through unconditioned spaces must be insulated. What is the principal reason for this insulation?
Where in a refrigerant circuit should a liquid-line filter drier be installed?
On a long refrigerant suction-line riser, what is the purpose of a P-trap (oil trap) at the base of the riser?
A cooling tower receives 95°F hot condenser water and discharges 85°F cold water on a 78°F design wet-bulb day. What is the tower "approach"?
In a heat pump, which component reverses the refrigerant flow to switch between heating and cooling modes?
A hot-water boiler make-up water line should be connected through which device to protect the potable water supply?
Installation Mechanical Systems
Per the Florida Building Code and ASME boiler code, the discharge from a boiler pressure relief valve must terminate:
What is the principal purpose of an expansion tank in a closed-loop hydronic heating system?
A chilled-water system needs to carry 60 GPM of water through a steel pipe. Using the common design guideline of 4 feet of head per 100 feet of pipe and a velocity target of 4–8 ft/s, which nominal pipe size is most appropriate?
The Net Positive Suction Head required (NPSHr) by a centrifugal pump is most directly related to which system condition?
A lift station serving a mechanical system uses a submersible pump discharging through a force main. What is the most critical installation practice for the discharge piping?
Pneumatic control air tubing is commonly made of which material, and what is a typical operating pressure?
When piping gasoline tanks and pump installations for a mechanical contractor's scope, which type of piping is most commonly approved for the underground fuel-carrying portion?
For pressure piping (such as a standpipe or process line), what is the purpose of a hydrostatic pressure test before placing the system in service?
A pipefitter needs to cut a 90° elbow takeout for a 6-inch standard pipe. The elbow takeout (center-to-end dimension) for a 6-inch 90° elbow is approximately 6 inches. What total length of straight pipe must be cut to make a run with a face-to-face dimension of 36 inches between two 90° elbows?
Per the Florida Building Code, Mechanical, what is required on a primary condensate drain line from air-conditioning equipment?
What is the minimum condensate drain pipe size required by the Florida Building Code, Mechanical for air-conditioning equipment up to about 20 tons?
Per NFPA 99, which material is most commonly used for medical gas oxygen piping in a health care facility?
Before placing a new medical gas pipeline system in service, NFPA 99 requires which test sequence?
When installing an outdoor air-cooled condenser, what minimum clearance is typically required around the unit for service and airflow?
Installation Refrigeration Hvac Equipment
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