Question Bank

#1

On a standard psychrometric chart at a fixed (known) total pressure, which pair alone can FIX the state of moist air?

Two independent properties (e.g. T_db + RH, or T_db + T_wb) locate the state (ASHRAE Fundamentals).

#2

The adiabatic saturation / wet-bulb process on a standard chart follows approximately which process line?

Sling/psychrometric adiabatic saturation tracks ~constant h (and ~constant wet bulb for air–water).

#3

The humidity ratio (W) in lb water per lb dry air (or g/kg) is a function of which pair in typical HVAC calculations at known pressure?

W from p_w = φ·p_ws(T_db) at total pressure P. ASHRAE Fundamentals equations.

#4

In a single-stage ideal vapor-compression cycle, the component that RAISES refrigerant pressure from evaporator to condenser is the:

Compressor does work; expansion valve drops P/T.

#5

Coefficient of performance (COP) for a cooling machine is classically which ratio?

COP_cool = Q_L / W_in (per thermodynamics and ASHRAE).

#6

Refrigerant R-410A is commonly classified in ASHRAE 34 (designation at time of this bank) in which flammability and toxicity class pair?

R-410A: historically A1 (verify current ASHRAE 34/EPA listings for the edition you adopt).

#7

Heating degree-days (HDD) integrate over time which simple comparison between outdoor temperature and a balance/base temperature?

HDD = Σ max(0, T_base−T)/24 per day, etc. — used for load estimation.

#8

For sedentary comfort, dry-bulb and mean radiant temperature are often combined in practice into which “operative” or similar index because both affect sensible heat loss from skin?

ASHRAE/ISO comfort: MRT and air temperature both matter; often rolled into comfort metrics.

#9

In commercial office duct trunks, keeping supply airface velocity in a “noise-friendly” range most directly limits which user complaint?

SMACNA: velocity vs. noise, NC/RC, diffuser selection.

#10

The total static pressure a supply fan must overcome typically includes the sum of which categories on the “longest/ index” run?

SP fan selection = external static per SMACNA/MCA tables + safety factor.

#11

For a fixed-diameter impeller, if pump speed increases by factor n (N₂/N₁), the shaft power approximately scales with what exponent on n in ideal affinity?

Affinity laws: Q₂/Q₁ = n, H₂/H₁ = n², P₂/P₁ = n³.

#12

For geometrically similar fans, if flow scales linearly with speed, the static pressure (head) in in w.g. (for same gas density) typically scales with speed to which power?

Fan similarity: p ∝ N², Q ∝ N, power ∝ N³ at constant ρ.

#13

An air economizer in commercial buildings in suitable climates is intended primarily to do what when outdoor air enthalpy is favorable?

90.1/Title 24 style: enthalpy/dry-bulb economizer logic to reduce cooling kWh.

#14

ASHRAE 90.1 minimum efficiency for unitary / packaged equipment is most commonly specified at standard rating points using which “seasonal/integrated” metrics for part-load operation (vintage 2010+ in many U.S. paths)?

90.1 tables list IEER, SEER, HSPF, EER, CEER, etc. by product class.

#15

ASHRAE 62.1’s ventilation “rate” procedure provides outdoor air to breathing zone based primarily on which combination in office-like occupancies (concept)?

62.1: R_p, R_a, zone and system OA calculation paths.

#16

A total-energy recovery wheel in an AHU mainly transfers which pair between exhaust and supply airstreams in summer cooling mode (conceptual)?

Enthalpy/ERV: sensible+latent transfer; frost control, bypass, filters.

#17

In constant-primary chilled water distribution, for the same load (Btu/h or kW) if the design ΔT across the cooling coil is increased, the required flow (gpm) must:

Coil/loop flow ∝ 1/ΔT at same load — energy efficiency and pump trade-offs.

#18

Domestic hot/cold water pipe sizing in practice limits maximum velocity in small branches to reduce most directly which problems?

IPC good practice: velocity cap for noise, erosion, surges.

#19

For a water coil where both fluids are unmixed and flow is not pure counterflow, the “effective” mean temperature difference is usually computed with which form?

Heat transfer texts: LMTD with F, or ε-NTU; ASHRAE chapters reference coil modeling.

#20

Commercial kitchen exhaust grease ducts require which primary combination of design features compared with ordinary return ducts in many adopted codes?

NFPA 96, local amendments: Type I hood, clean-out, clearances, suppression.

#21

A direct-digital (DDC) field controller for RTUs typically actuates and monitors which of the following at minimum?

BAS/DDC: points list, I/O, sequences of operation per ASHRAE Guideline 0 practice.

#22

In modern facilities, the native objects (AI, BI, BO, etc.) in BACnet most directly represent which information layer between devices and a head-end?

ASHRAE/BACnet: open protocol object model for field integration.

#23

A thermostatic expansion valve (TXV) primarily controls which parameter at the evaporator outlet in steady service?

TXV/TEV: holds reasonable superheat; EEV similar with electronic control.

#24

A hot-gas reheat on a dehumidification coil in comfort applications is most often used to do what to leaving air?

Reheat/DOAS design: dehumidify then reheat to neutral supply.

#25

Duct leakage class in standards like SMACNA/ASHRAE is commonly expressed in terms of cfm/ft² of surface at a reference static pressure, which is intended to improve what?

Leakage classes (e.g. A/B/C) reduce unintended OA/return losses — SMACNA.

#26

Turning vanes in large rectangular elbows primarily reduce which quantity compared with a hard mitered turn?

Fittings + vanes: static regain / lower loss; SMACNA loss coefficients.

#27

Demand-control ventilation in occupied zones often modulates minimum outdoor air based most directly on which common proxy when approved by the code path?

DCV/IEQ: 62.1+90.1 allowed approaches with CO2-based reset, minimum OA floors.

#28

In a variable-primary-flow chilled water plant (no decoupler bypassing full flow in idea), a VFD on the chiller pump is primarily modulated to maintain what, subject to chiller mfr limits?

VPF: chiller mfr min flow; DP or ΔT control at plant.

#29

On a water cooling tower, “approach” is most commonly the difference between which two values?

CTI/ASHRAE: approach = T_cw, out - T_wb,in (approx) for a given L/G.

#30

Air-to-air or air-to-water heat pumps in cold, humid conditions periodically run defrost to remove frost from the outdoor coil to restore what?

Defrost: reverse, resistive, or off-cycle per OEM — restore UA and flow.

#31

A blower-door test measures envelope leakage at 50 Pa reference and is often used to compare homes and small buildings. It helps estimate what for mechanical engineers?

Infil exfil / ACH50 mapped to model inputs per standards.

#32

The “ventilation rate” procedure in ASHRAE 62.1 is distinct from the IAQP in that the rate procedure prescribes which starting point (conceptual)?

62.1: VRP vs IAQP paths, local adoption.

#33

Cavitation in centrifugal water pumps is primarily controlled by keeping available NPSH (NPSHA) in relation to the pump’s required NPSH (NPSHR) in which way at the design point?

HI/PI: NPSH margin on curves for hot/chilled/cond water.

#34

A diaphragm or bladder expansion tank on a closed hydronic system primarily accommodates what, when loop temperature and fluid volume change?

HVAC hydronics: point of no pressure change + expansion tank design.

#35

When a building reduces internal lighting power density, the “knock-on” effect on the HVAC system may include which of the following (conceptual)?

EAp2 style: LPD interacts with reheat, plug loads, internal gains.

#36

A capillary tube or fixed-orifice in small sealed domestic refrigeration is primarily fixed for which operating envelope compared with a TXV in larger split systems?

Cap-tube: cheap, but narrow envelope; TEV/EXV: control.

#37

A VAV air terminal with hot-water reheat is selected at design so that, at the zone peak sensible load, it can (conceptually) do what in parallel with the central supply SAT reset?

VAV reheat+SAT reset: avoid cold-deck/zone mismatch.

#38

Laboratory/healthcare exhaust classified as “contaminated” in code paths must not be recirculated; which fundamental arrangement must be preserved?

62.1+NFPA/ICC: exfil, stack, and separation tables.

#39

When a central plant serves many AHUs, “diversity” in peak load calculations accounts for the fact that not all zones will peak in which way?

Diversity/coincident vs non-coincident loads in CUP.

#40

Split air-cooled condensing units in very low ambient (cold) operation often add head-pressure control to avoid which problems?

Head pressure/ fan cycling / VFD condenser fans: maintain stable condensing for expansion device.

#41

A hydronic heating boiler in commercial service requires pressure relief to limit vessel pressure. The set pressure of the required relief device is normally established based on which authority chain?

Boiler Mfr + ASME + state/province law for relief valves.

#42

A condensing boiler gains higher AFUE/thermal efficiency by recovering latent heat. This requires the return water temperature to be in what relation to the flue-gas acid dew point (conceptual)?

Return below dew point: condense flue; condensing design vs material corrosion controls.

#43

In a low-pressure steam system serving preheat or humidification, a primary role of a steam trap at the end of a coil is to (conceptual)?

Steam trap selection per ASHRAE/SMACNA/Steam guides.

#44

A MERV-13 (or ePM1 per ISO 16890) filter for general ventilation is more restrictive than low-MERV disposables. The primary IAQ/energy trade-off it introduces is (conceptual)?

MERV+fan laws: kWh vs particles (52.2 / ISO16890 / ASHRAE 241 context).

#45

In-duct UV-C in AHUs, when validly designed, primarily targets inactivation/ reduction of which concern on the wet cooling coil/ drain pan, subject to product listing and IAQ goals?

GUV: coil hygiene + pathogen; still meet OA and filtration.

#46

Open-plan office ceiling diffusers in ASHRAE/NC design practice are most often selected to keep room noise in which framework at design CFM/NC curves?

HVAC sound: diffusers+silencers+paths per ASHRAE Applications.

#47

Large roof-mounted AHU/RTU in sensitive buildings is typically mounted on spring isolators with bases to (conceptual)?

Isolation: spring deflection vs rpm, seismic snubbers, flexible connectors.

#48

The continuous air barrier in the building thermal envelope, when well executed, most directly benefits HVAC energy in which way (conceptual)?

90.1+energy models: air barrier affects infiltration/ventilation balance.

#49

Fire/smoke dampers in duct penetrations of rated assemblies are interlocked in life-safety paths primarily to (conceptual)?

Dampers+detectors+AHU interlocks: fire EOR+AHJ.

#50

A three-pipe (heat-recovery) VRF/VRV system, compared with two-pipe, allows different indoor units on the same refrigerant system to (conceptual)?

3-pipe HR VRF: heat recovery; charge limits+pipe length tables.

#51

For occupied machinery rooms with refrigerant charge above threshold in many codes, which combination is a central safety requirement in ASHRAE 15/34 spirit?

15/34+EN 378+local: MRV/ERV not substitute for 15; leak detection+fan.

#52

When ethylene/propylene glycol is added to a hydronic loop, the most important design adjustment vs pure water, besides freeze protection, is (conceptual)?

Glycol: density,cp,viscosity, chemistry — larger pumps, coils.

#53

In HVAC hydronic line sizing, if equivalent length of fittings greatly exceeds straight pipe in a branch, the designer should (conceptual)?

Cameron/Crane: equivalent length + C factors.

#54

In enclosed parking, mechanical exhaust is most commonly controlled/ verified by (conceptual) which sensor strategy with IMC/UL paths?

ASHRAE/ASHRAE 62+IMC: engine exhaust vs dilution+CO.

#55

Dedicated toilet/change-room exhaust in commercial buildings in many codes and 62.1 is intended primarily to (conceptual)?

62.1+IMC: cfm, makeup, and DO NOT recirc in many paths.

#56

IEER (integrated) for unitary products differs from a single EER at one capacity point in that it (conceptual)?

IEER/SEER/SCOP from AHRI methods — design vs annual.

#57

A water economizer in a chiller plant may precool/reduce lift by using (conceptual) which resource when it is “cooler” than the condenser or cooling tower approach allows?

WSE: HX in series/parallel, fouling+freeze protection in cold climes.

#58

A negative-pressure TB isolation or AIR isolation room, per healthcare ventilation guidance, is achieved primarily with which of the following (conceptual)?

170+FGI: room pressure+ACH+filtration+temp.

#59

An ultraclean/ISO-class critical OR HVAC diffusers aim primarily to (conceptual)?

170+USP: HEPA in critical, airflow patterns, test/cert.

#60

A2L refrigerant charge limits in occupied spaces are set to limit which two coupled risks, subject to the adopted standard+product listing?

A2L: charge/m², m³, and leak detection+mech room ventilation.

#61

Fundamental Cx/functional testing of a central plant before handover is intended primarily to (conceptual)?

G0+G1+185: functional tests, trend logs, PFC.

#62

A TAB report on a variable-air AHU in full balance typically documents which of the following as primary verifications of design intent (conceptual)?

NEBB/TABB: OPR+design vs measured air/water+controls.

#63

In hydronic proportional balancing, the key idea is to set circuit balancing devices so that (conceptual) what holds across parallel branches at design (or set) condition?

GPM balance: set balancing valves+indexing paths.

#64

Advanced (interval) metering of HVAC+whole-building demand is used in energy program paths primarily to (conceptual)?

ASHRAE+GBCI+utility: M&V, FDD+interval data.

#65

A rules-based FDD in BMS (e.g. “SAT>set+deadband+full cooling”) targets which category of problem first?

FDD: OAT vs SAT vs valve position vs reheat+spec.

#66

In high-density colocation, raising cold-aisle setpoint (within the ASHRAE/TC9.9-like envelope) generally reduces chiller/CRAH energy, but is bounded by (conceptual)?

TC9.9: T/RH+operational envelope+free cooling+water vs air.

#67

A cold-aisle + hot-aisle with aisle containment, compared with a fully mixed room, most directly improves (conceptual)?

Containment+blanking+CFM/thermal discipline.

#68

A cooling-tower water treatment program that allows too few cycles of concentration in hard water, without blowdown control, can lead most directly to which two coupled problems in condenser/ tower loops (conceptual)?

ASHRAE 188: WMP+testing; cycles+blowdown+inhibitors+filtration+UV.

#69

A sidestream sand filter+UV on a condenser water loop, together with a water treatment spec, is intended primarily to (conceptual) reduce which combined risks?

Cooling water: COC, pH+inhibitor, drift eliminators+UV+sidestream.

#70

A multi-chiller plant with VFD compressors+sequencing is most often optimized in controls to (conceptual)?

CUP optimization: chiller+aux loads; lift; tower+cond water reset.

#71

A 4-pipe WSHP in a two-pipe changeover loop, compared with 4-pipe all-season, (conceptual) is limited by which primary constraint in shoulder seasons in many designs?

Changeover+GHX+loop temp+cascade heat pump.

#72

Two identical pumps in parallel, compared with one, at a common system curve (conceptual) tend to (which behavior)?

Parallel+series pump curves+system+Affinity vs parallel laws.

#73

A continuous radon/IAQ+ventilation strategy in basements+ASHRAE 62.1 is intended primarily to (conceptual)?

RC/EPA+62.1+local: IAQ+ventilation+sub-slab.

#74

Some “advanced IAQ” devices (e.g. PCO) must be vetted in projects because, if poorly specified, they can (conceptual) produce or fail to control which IAQ byproducts?

Caution+listing+62.1+O3 limits in devices.

#75

A transcritical R-744 booster rack in a supermarket, compared to subcritical R-22 legacy, (conceptual) has which distinctive thermodynamic+design trait?

R-744: Tcrit, gas cooler+HP+heat reclaim.

#76

Static pressure reset and lower SAT on a VAV+AHU are limited in practice to avoid IAQ/comfort issues. The primary bounds are (conceptual)?

Resets+limits+reheat+hum+OA+comfort—never unlimited.

#77

A layered IAQ + respiratory-mitigation strategy in buildings (when adopted locally) most typically combines (conceptual):

Layered+engineered+verify AHJ+pathogen+filtration+OA.

#78

Post-occupancy training, M&V, and formal O&M handover in LEED/ASHRAE-style programs mainly preserve (conceptual) what, versus first-year peak performance+design intent?

M&V+O&M+FM+re-Cx+OPEX—persist savings and intent.

#79

When contract documents “adopt” ASHRAE, IPC, NFPA, and EN references alongside local and owner standards, the defensible first step to resolve a conflict (conceptual) is:

Hierarchy+law+AHJ+stamped+contract+exceptions+document+PE+owner+AHJ+path.

#80

For systems with near-equal first cost, a registered PE+owner+proforma+contract path most defensibly uses which of the following (conceptual) as a primary LCC+NPV+O&M selection filter+design basis?

LCC+NPV+OPEX+O&M+spares+utility+failure+risk+PE-stamped design basis—capstone for equal first-cost options.