The six weeks when nothing is right

On a spring or autumn day the sun does most of the heating. A south and west elevation gains heat all afternoon while a north elevation loses it all day, and the difference between the two sides of the same floor can be larger than anything the system is being asked to make up.

If the building is on a two-pipe system it can only be in one mode at a time. Whichever mode it is in, it is wrong for one side. That is not a failure of the equipment; it is what the system was built to do.

• Check the sensors. One in direct sun on a west wall will drive a whole zone wrongly for six weeks a year and correctly for the rest, which is why nobody catches it.
• Check the zoning against the elevations. If one zone spans north and south, it will never be right. Splitting it is real work and it is sometimes worth it.
• Blinds and solar film do more for this than any control change, and neither is our work.
• Balance the air if it is a ducted system — often one side is simply getting more than the other for reasons nobody documented.

We will not tell you a control adjustment makes a two-pipe building comfortable on both elevations in April. It does not. What it can do is make it less wrong, and make the mode change at a better time of day.

The gap between the heating setpoint and the cooling setpoint — the deadband — is too narrow. On a day that starts cold and warms up quickly, the building crosses it, and the system dutifully does both within a few hours.

It is worth knowing this costs real money. Heating a space in the morning that you then pay to cool at noon is the most expensive thing a building can do, and it is invisible unless somebody looks at the controls.

• Widen the deadband so the building coasts through the middle instead of fighting. The right width depends on the building and its occupants — we will not print a number.
• Use outside air. If there is an economiser, a spring morning is exactly what it exists for. A stuck one is common and invisible.
• Look at optimum start. Bringing the building on too early on a day that will be mild by nine is a straightforward setting.

If the deadband is already wide and it still swings, something is calling that should not be — a stuck valve, a failed sensor or a control fault. That is a visit, and it is worth making because it is costing money every day it continues.

In the shoulder season a building can sit inside its deadband all day, which means the system barely runs — and in most buildings the fresh air arrives with the heating or cooling. No call for either means no air movement, no outside air, and a space that is the right temperature and still feels stale.

It is the complaint most often reported as “the air conditioning is broken” when the air conditioning is working perfectly and simply has nothing to do.

• Run the fans on occupancy rather than only on a call for heating or cooling. On most systems this is a setting.
• Check the outside air damper is opening at all. A minimum position that has drifted to zero is common and nobody notices in January.
• Measure what is actually being delivered rather than assuming from the schedule.

Running the fans continuously uses electricity, and on some systems it also brings in humidity. It is a trade, not a free improvement, and we will say which way it falls in your building rather than selling it as a fix.

Cooling equipment removes moisture as a side effect of cooling. On a mild, wet day there is very little cooling to do, so the system barely runs, so it removes almost no moisture — while the outside air coming in is close to saturated. The building ends up cool and clammy.

This is the shoulder-season complaint with the least straightforward answer, because the equipment is behaving exactly as designed and the weather is doing the rest.

• Make sure the system is not oversized. An oversized system satisfies the thermostat in minutes and never runs long enough to dehumidify at any time of year. This is the root cause more often than anything else.
• Check the outside air quantity. Bringing in far more than the building needs, on a wet day, is bringing in moisture for no benefit.
• Check that the fans are not running continuously in this weather — which is the opposite of the advice on the previous complaint, and that is the point: they are different problems.

Where a building genuinely needs moisture removed in mild weather, that is dedicated equipment and it is a project, not an adjustment. We will say so and price it properly rather than promising a control change will do it.

On a two-pipe building the switch from heating to cooling is a physical changeover, and going back is not a five-minute job — it can take a day or more to drain, refill and rebalance. So it gets done on a date rather than on the weather, and Buffalo does not respect dates.

Somebody made a reasonable decision in the second week of a warm April, and then the first week of May was cold.

• Change how the date is chosen. Basing it on a forecast run rather than a calendar entry is free and it helps more than anything else on this list.
• Keep supplementary heat available in the spaces that suffer — typically north-facing and top-floor. Knowing which those are in advance is a survey, not a guess.
• Check what changeover actually costs you in hours. If it is genuinely a day of work, that is the constraint, and it is worth knowing before the argument.

If the building is cold after changeover in genuinely mild weather, that is not the season — that is a valve, a pump or a control that did not follow the changeover. Worth a visit, and usually a quick one.