School Heating Investigation
One of our most challenging projects was to find out why a recently completed senior school heating system had failed to heat some of the classrooms and ancillary rooms. Not all the rooms were cold, the problem was intermittent but irritatingly the main hall required constant heat to retain temperature.
We set to work, planned a survey of the rooms and the service areas especially the ducted sections between floors and adjoining buildings. Drawings were available, and we looked carefully over the installation; two hot water circuits both connected to modular boilers each fitted with variable speed pumps. To prevent surges in the water flow, each boiler was fitted with a ‘low-loss header comprising two large diameter pipework sections several meters in length connecting the flow and return from auxiliary circuits around the buildings. The rooms and offices split were divided between separate buildings. Fan coil units in one building supplied from a variable temperature circuit, the other building with a constant temperature circuit to radiators. The two circuits delivered heated water to fan coils mounted at high level to each room.
The classrooms, built to the latest building specifications had ‘U’ factors between 0.14 and 0.22 watts/meter/K and similarly the glazing to the classrooms, also having a low U-factor. The pupils and teachers delivered the majority of the ‘heat gain’ apart from the kitchen areas which had a variety of appliances for warming and cooking of meals.
Using some fairly rudimentary judgements and analysis we reviewed the heat loses for both the buildings at a minimum outside air temperature which the boilers were clearly able to overcome. We checked the heating load requirement for comfortable conditions and reviewed again the radiator and fan coil dimensions in the classrooms. The heat was clearly achievable. The complaints were, well, otherwise. Class A next to Class B was barely warm and so were the fan coils and radiators, however on the opposite side of the corridor the rooms were comfortable, so what was happening?
The next part of the mystery could well have involved pipework sizes, so we checked the minimum design flow for the fan coils and radiators to provide a low resistance flow at the design heating temperatures. This was applied to all the main branches and the many take-off points for the radiators and fan coil units. Importantly, the variable speed pumps were extremely powerful with plenty of pressure available to reach the extremities of the distribution network. Oddly, both pumps operated at their design pressure almost continuously, this prompted another question, why again was the heat not reaching the classrooms. We learned from our customer that when the temperature fluctuations commenced it was often accompanied by much adjustment and wide openings of flow valves to allow their maximum heat in the classrooms before the commencing lessons. This action clearly exacerbated the starvation of flow from one room or rooms for the sake of the others.
Our attention was turned to the controls and an area beyond our scope of work, however, aided by the able services team on site, we asked why the pump connections to the controls system was not connected, another job to do? Fan coils in the main hall had an air distribution problem rectified by de stratification which we recommended instead of a re design of the fan coil units. One area also suffering from a lack of heat was fitted with radiant heat panels which required hotter water entering temperatures for improving efficiency, not a simple task requiring a changeover of equipment. We signed off with a recommendation that the balancing of the radiators, the only course of action remaining; was investigated and that was our parting recommendation to services the team.