Scheduling is often the single biggest factor causing excessive levels of energy consumption. It is typically the ECM (energy conservation measure) that has the most effect with the least investment. A building with no schedule will see an energy consumption decrease of up to 30% (sometimes more) when a schedule is instituted. While it would seem like common sense to turn off equipment when it is not needed, sometimes a deeper look is warranted to see why there is no schedule or if there are further scheduling opportunities.
For the purposes of this discussion, scheduling generally refers to hvac and domestic hot water equipment, though for facilities that can be shut down for extended periods of time (seasonal, extended breaks etc.) other equipment can be considered.
A simple indicator to assess the viability of hvac scheduling is the presence of manual thermostats. The majority of the time when these are present, there are immediate scheduling opportunities. These are very frequently found in schools, office buildings etc. This is the worst possible scenario; now the equipment sometimes runs 24/7 and there is no control over the set points.
For optimum hvac scheduling, either an EMS (energy management system) or programmable thermostats needs to be installed. Limit access to these, so schedule control is consistent. If no EMS exists, timers can be used for water heaters. Electronic timers have the advantage of time resetting after a power outage (mechanical timers will alter the schedule every time a power outage occurs).
Sometimes it is best to take a step back and think about the reasons for scheduling an hvac system to operate in the first place. A typical k-12 school can sometimes present many opportunities regarding scheduling.
A school has hvac to improve the learning environment. Many of us that are a bit longer in the tooth will recall that this is a fairly recent development, gaining traction in the last 30 years or so. That being said, hvac helps keep students attentive for longer periods of time. When this learning environment is no longer necessary, the hvac should be scheduled to go to non-occupied set points. Many schools do operate this way, and when the students leave, non-occupied set points go into effect. Often though, I see huge schedule discrepancies between similar schools. Some schools schedule the hvac to back off immediately after teaching hours but others leave the hvac operating for many additional hours for janitorial services or late teachers. This is unnecessary. Even schools with a terrible building envelope will hold temperature for a few hours. It does not get hot or cold right away. Having established business hours for the hvac system let’s the teachers know that they can stay if need be, but the environment could change.
At this point I would like to discuss non-occupied set points. I prefer to keep those as aggressive as can be: 85F-90F for cooling and 55F to 60F for heating. If humidity control is an option, that is even better for humid environments, since the hvac will only come on if humidity levels increase to set point. In extremely mild climates, turning the hvac totally off could be considered, though aggressive non-occupied set points should accomplish the same thing and cover any weather anomalies. In the humid south, the only real reason that hvac in schools is operated in the summer is for mold control. Once building characteristics are understood and there is knowledge about how the building temperature drifts without hvac, one has a better idea of how aggressive the non-occupied temperatures can be. Some control strategies (to be discussed later) will actually determine start-up times automatically (this will change as the non-occupied set point is changed). Savings are generally 1% for each degree the set point is set back per 8-hour period (http://energy.gov/energysaver/articles/thermostats).
Let’s assume that a facility will not budge on reduced scheduling for janitorial services (lead janitor has a brother on school board, etc.… (haha)). At that point it would be wise to dissect the actual cleaning activity and look for opportunities there. Leaving a whole building operating while the halls are cleaned one at a time is a total waste; schedule the halls to operate only as they are being cleaned.
If the cleaning service is contracted out, simply state your hvac scheduling intentions in the contract. There will be a company that will have no problem with it, since there are far worst environments than a slightly warm or cold school or office building.
If a hard stance on operating hours seems too draconian for a particular work culture, technology can come to the rescue for many situations like this and other scheduling anomalies: Install an override for the hvac system.
An override is a button that operates the hvac system for a pre-determined amount of time. Often 4 hours is used as a default for overrides, but I recommend 1-hour settings. This allows for much tighter scheduling, and the button could be pushed again if more time is needed. An override is a useful option that prevents having to make continual small scheduling changes (can you imaging trying to adjust the schedule daily for every employee that needs to stay late) and decreases the chances of forgetting to return the schedule to normal.
Multi-use facilities are ideal candidates for overrides. Churches in particular sometimes let other organizations (such as weight watchers, boy scouts, AA etc.) use their facilities. These organizations should use the override for their hvac. This takes the scheduling burden off the church and ensures only the amount of hvac that is needed is consumed.
The picture below was used as a training tool when an override system was put in place. There were a few employees at this engineering firm that enjoyed working all hours of the night. Instead of leaving the hvac for the whole building operating 24/7, the overrides allowed only the occupied area hvac systems to be operated.
Many times there are hidden opportunities within a schedule. Some schools have actually scheduled the hvac system to be off during lunch hour. Though this may not seem like much, it was noticeable on the utility bill.
Multiple building campuses have their own set of challenges. A good example of a complicated campus to schedule would be a university. It is very important to know the energy utilization index (sometimes called energy intensity, this is the energy consumption per square foot) of each building, so the least efficient building is operated the least, if possible. If certain classes can be taught at multiple buildings, it would be wise to schedule the most efficient building first. Proper space planning can go a long way for facilities such as this. It makes no sense for 3 buildings to be operated partially empty when one building could do the job. Having a designated person or system in place for complicated scheduling like this will pay huge dividends. Any additional manpower costs will be paid for by energy savings (and then some).
I will give another example of the occasional need to step back and ask if hvac is needed.
This is a case of good intentions that could cause a bad outcome.
The picture below is from a welder training facility. The building is air conditioned, and concurrently leaves the overhead door open and runs the exhaust fans to maximize air- flow. Obviously, this is a very bad scenario.
The question is: why would a welder training facility be conditioned? As a former industrial maintenance manager in multiple facilities that had welders, both direct and contract, working for me, I can say from experience that it is very rare for a welder to ever work in a conditioned facility. The best that can generally be hoped for is to have a man-fan and sometimes, if the task is small enough, to be able to carry the work outside and weld it (though that is rare). By training these potential welders in such an artificial environment as this, the risk is they graduate and realize they cannot stand the working conditions that they will be subjected to, or that they will not be in the habit of proper hydration (or be familiar with cooling technologies such as cool vests and compressed air suits) and adequate breaks to prevent heat exhaustion or worst. A good analogy to this would be to train in Alaska for a marathon in Miami!Google+