Open-Plan Comfort: Thermal and Acoustic Trade-Offs
An 1,800 m² open-plan technology office houses 160 hot-desking staff. Post-occupancy surveys show 38% dissatisfied with temperature; measured PMV is +0.7 in the west zone, air speed is 0.05 m/s, and radiant temperature asymmetry near the perimeter glass is 6°C. The landlord controls the HVAC and refuses setpoint changes. Noise measurements show NC-42, reverberation time of 0.9 seconds, and frequent complaints about speech privacy. The tenant wants WELL v2 certification and has budget for either local thermal comfort devices or acoustic treatment, not both at full scale. The lease gives the tenant control over furniture and ceiling finishes but not the base building. The project is pursuing Thermal Comfort 02, Sound 04, and Sound 05, and the team must decide which measurements to repeat after interventions.
1. Diagnose the thermal comfort failure and determine whether the space can satisfy Thermal Comfort 02. Prioritize interventions under the budget constraint.
Read the worked answer
Diagnosis: a PMV of +0.7 is outside the ASHRAE 55 comfort range of roughly -0.5 to +0.5, and 38% dissatisfaction exceeds the typical 20% threshold used in Thermal Comfort 02. The low air speed of 0.05 m/s and 6°C radiant asymmetry near the glass point to a combination of solar gain, poor air mixing and no local control. The space is warm and stagnant near the perimeter, and occupants cannot adjust their own conditions.
Does it satisfy Thermal Comfort 02? Not on these measurements. The feature expects documented thermal performance and occupant feedback; a survey alone does not compensate for measured conditions outside the comfort range. The project should treat the survey and the physical measurements as linked evidence.
Priority interventions:
- Solar control: shading, film or blinds on west-facing glass to reduce radiant asymmetry and solar gain.
- Air movement: ceiling fans or desk fans to raise air speed within comfort limits. This is often the lowest-cost way to improve perceived comfort without changing the base-building setpoint.
- Local control: if the lease permits, add local diffusers or zoning in the west zone. If not, document the landlord constraint and show how tenant-controlled measures compensate.
- Layout: move workstations away from the perimeter glass where asymmetry is highest.
Budget judgment: thermal fixes address the larger dissatisfaction rate and the precondition risk. Acoustic treatment can be phased, but the team should not spend the entire budget on acoustics while Thermal Comfort 02 fails. Low-cost acoustic measures can be combined with thermal fixes if the budget allows.
2. Diagnose the acoustic issues and select measures that address both the NC-42 and the 0.9-second reverberation time.
Read the worked answer
Diagnosis: NC-42 is high for open-office background noise, and a 0.9-second reverberation time indicates too many hard surfaces. The combination reduces speech privacy: sound persists and travels, so nearby conversations are intelligible and distracting. The problem is not simply loud HVAC; it is the interaction of background noise, reverberation and layout.
Measures:
- Absorption: add sound-absorbing ceiling tiles or baffles, wall panels and soft furnishings. Target the ceiling first because it has the largest surface area.
- Layout: separate phone and collaboration zones from focused work; use screens or partial-height partitions where appropriate.
- Sound masking: add a well-designed masking system after reverberation is controlled. Masking before absorption can make the space louder without improving privacy.
- HVAC: if NC-42 is driven by air handling noise, ask the landlord to verify fan speed, duct lining and diffuser selection. If the landlord will not act, document the constraint and use layout and absorption to reduce impact.
Verification: re-measure NC or RC in the same locations and operating conditions, and re-measure reverberation time. Record occupancy and HVAC mode. For Sound 04 and Sound 05, use calibrated instruments and compare before-and-after data rather than relying on subjective impressions.
Budget judgment: if only partial acoustic treatment is possible, prioritize ceiling absorption in the noisiest zones and layout changes. These address both metrics more efficiently than masking alone.
3. How should the team document the landlord constraints and verify results after interventions?
Read the worked answer
Document landlord constraints: include lease excerpts showing which systems the tenant controls, correspondence with the landlord about setpoints and HVAC noise, and a clear statement of what the tenant can and cannot change. Do not present tenant-controlled measures as if they were base-building fixes.
Verification plan:
- Thermal: repeat PMV/PPD or occupant survey after interventions; measure air speed, radiant temperature asymmetry and operative temperature in the same zones and seasons. Record clothing and activity assumptions.
- Acoustics: repeat NC/RC measurements and reverberation time in the same rooms, with the same HVAC mode and occupancy conditions. Document instrument calibration.
- Occupant feedback: use a short survey before and after to show whether complaints changed, but do not substitute satisfaction scores for physical measurements.
Documentation package: survey results, measurement reports, intervention specifications, photographs of installed measures, invoices, landlord correspondence and a corrective action log. If the landlord refuses a setpoint change, state that limitation and show how fans, shading, layout and local control reduced dissatisfaction. If results still fall short, the team should not claim the feature is met; it should document the residual risk and consider whether a different space or lease negotiation is needed.