Space Heaters in a New VAV Building

Most likely a zoning and control problem with a solar-gain component, not a single bad setpoint.

Reasoning:

• A core thermostat controlling a west perimeter zone will hold the core at 23°C and let the west zone drift. The west sensor reading 24.5°C while occupants report 26.5°C suggests the sensor is not where the people are, or is not the control sensor.
• Summer 26.5°C and 62% RH points to solar gain plus insufficient cooling or airflow at the perimeter, with humidity near the upper comfort bound.
• Winter 20.5°C at 9 a.m. in the same zone points to a heating problem - fin-tube output, reheat, or morning warm-up - which is why 14 space heaters appeared. The heaters are a symptom, not the disease.

Data to collect

• Operative temperature with a globe thermometer at 0.6 m and 1.1 m in the west zone, plus air speed.
• VAV box airflow (min/max), damper position, and reheat valve position at 8 a.m. and 3 p.m.
• Supply-air temperature and zone sensor calibration.
• Solar radiation or window luminance at the west facade in the afternoon.
• Clothing and activity assumptions used in the model.

What would change the diagnosis: if the VAV box is at maximum airflow and the zone is still warm, it is a capacity/distribution problem. If airflow is at minimum, it is a control problem.

Order by cost and impact:

1. Fix sensor location and zoning. Move or add a temperature sensor in the west occupied zone and control to it, or split the perimeter into smaller zones. This is inexpensive and may resolve the afternoon drift.
2. Check and reset VAV minimums and reheat. In cooling, minimum airflow may be too low for the west zone; in heating, the fin-tube or reheat may be undersized or not sequencing correctly at morning warm-up.
3. Address solar gain with exterior or interior shading on the west facade - this reduces both the afternoon temperature and the cooling load.
4. Humidity: 62% RH in summer suggests the coil or supply-air temperature is not low enough for dehumidification, or the space is over-cooled elsewhere to compensate. Evaluate dedicated dehumidification or supply-air reset only after steps 1–3.
5. Space heaters: do not ban them first. They are evidence of unmet heating. Set a date by which the fixes should make them unnecessary, and provide a temporary safe alternative (properly sized, thermostat-controlled, with fire and circuit-load review).

The energy manager's resistance is a constraint, not a reason to skip the diagnosis. Fixing zoning and reheat sequencing often costs less energy than 14 space heaters.

Survey design

• Use a validated thermal comfort survey (ASHRAE 55 / ISO 10551 style) with the seven-point thermal sensation scale, plus a satisfaction question and a preference question.
• Sample by zone, not building-wide; the east zone is the control group and should be surveyed too.
• Record clothing, activity, and location at the time of the survey.
• Run it at 9 a.m. and 3 p.m. in both seasons, because the complaints are time-dependent.

What to do with results

• Compare predicted mean vote from measured conditions to actual votes; a large gap points to a non-thermal cause (drafts, radiant asymmetry, humidity) or to control frustration.
• Use the percentage dissatisfied by zone to prioritize capital.
• Repeat after fixes; do not declare success from a single survey round.

Note: meeting the model's ASHRAE 55 claim at design conditions does not mean the as-operated building is comfortable. The model is a starting point, not evidence.