Technical

There are at least 21 different faults that a Fan Coil Unit can have. In our experience it is very common in maintenance callouts for fault to be repaired inaccurately. The immediate problem may be temporarily fixed, but the solution is short term and does not work in all seasons. As an example of this a common problem is FCUs being permanently in heating or cooling. These units often pass a standard maintenance test.  Changing the temperature may work short term but is not a permanent solution. We aim to provide systems that are 100% correctly maintained. This can be a long term project. In the short term we use the control technology to minimise the effects of any faults.

Health effects of CO2 levels

Ensuring that all elements of the system operate at the correct times is important for comfort and efficiency. We operate the following efficiency modes to support this. Early Morning Start Routines The system starts at the correct time each day, depending on the internal temperature and the weather. End of Day Stop Routines Our systems use a smart slows down and stop routine to ensure that it is using all the energy stored in the system by the end of the day. Bank Holidays and Weekends Offices often have reduced or nil staff at Weekends and Bank Holidays. Programming the 9 annual Bank Holidays with a holiday schedule rather than a work schedule saves 2.3% energy. Motion detection Occupancy detection by motion sensors, often linked to the lighting system, aid efficient start stop times, particularly in low occupancy offices.

We correlate all tenant issues against real time BMS and maintenance data, allowing us to for instance discern the difference between ‘Cold’ that it a draught, over cooling or a lack of heating. This enables accurate adjustments to improve comfort.  

A cooling system in a commercial building typically consists of a Chiller, which works like a giant fridge, transferring cooling energy to water. The water is pumped around a primary circuit containing just the chiller. Energy is removed from this primary circuit to a secondary circuit around the building to Fan Coil Units and Air Handling Units. These have heat exchangers moving energy from water to air to keep you cool. The efficiency of this entire process is complex. However by being efficient, you can save money, be more comfortable and make all the equipment (which is expensive) last years longer. Areas where performance have been improved are: Maintenance. Ensuring that energy is not lost by direct heat exchange from hot to cold water. Ensuring energy is not unnecessarily lost to dehumidification. Ensuring that unnecessary energy is not lost to friction as fluids move. Maximising the efficiency heat exchangers. Reducing heat losses from mechanical equipment. Ensuring that equipment does not remain hot at night. This can cause damage to stationary equipment, for instance to bearings. If you are interested in discussing the more detailed technical aspects of this, please get in touch.

This graph shows the temperature distribution at 2pm on several days on one of our sites where there are 160 temperature sensors. The lower temps are empty meeting rooms. The higher temps are located next to a bank of screens. All temperatures in working areas are 22-24 deg. Areas above 23 generally feel cool enough at desk level because there is chilled air circulating. On an average day with 400 people working on site, there are zero ‘aircon’ requests to the facilities team. Facilities will receive occasional requests when there is unseasonal weather (its cold in summer, or very sunny in winter) or when there equipment failures. Before our work to improve this system, there were ‘aircon’ requests every day.

Heating and Cooling systems are usually designed for the maximum capacity event. This ensures that there is enough heating on the coldest day in winter and enough cooling on the hottest day in summer. Most days in UK are quite temperate. This graph shows average max and min temp over the year. Real time weather compensation is both more energy efficient and more comfortable. People do not like anti-seasonal heating or cooling. We set up systems to be more temperate.

Fan Coil Units choose how much heating or cooling energy to produce using Proportional Integral Control. As temperature gets further from setpoint, the fan works harder. This is the Proportional. If the temperature is not getting close to setpoint after a time, the fan works harder. This is the Integral. Deadband is the range around the setpoint where no heating or cooling occurs. The balance of Proportional, Integral and Deadband is very important to comfort. We analyse every temperature complaint, correlate it with the data at that particular time, whilst assessing the condition of the FCUs. This has given us an excellent understanding of how to set up a control system to be comfortable.

In the UK, the temperature outside is usually less than the temperature inside! The ‘Free Cooling’ available from the lower outside air temperature is often not utilised. Most control systems will require chillers to be on, even when the outside temperature is nearing zero, in order to combat the internal heat gains. It is not realistic to open the windows or pump cold air direct into the office on cold days as this is not comfortable. However, plant systems often have the ability to make best of ‘Free Cooling’ available from cold outside air through the chillers, AC units or air handling unit. Maximising the use of these can provide significant savings.        

In demand led operation the control system asks for heating from Boilers or cooling from Chillers. In principle this is quite simple and most control systems do it. In practice many control systems will keep the boilers and chillers on most of the time during office hours. Often this is caused by minor faults such as mis-calibrated temp sensors, ‘aircon’ faults or a temperature setting error. A well managed ‘Demand Led’ building will use boilers in midwinter, chillers in midsummer and on temperate days boilers may be required in the morning with chillers in the afternoon. There are some cases where boilers and chillers are required at the same time…for instance sunny days in winter. Well managed Demand Led systems are very efficient. The energy savings can significantly outweigh the cost of implementation.