Heating, cooling and integrated thermal services

A load is a required rate of service

A heating load is the rate of heat addition needed to maintain specified conditions in the chosen model. Transmission, outdoor air, solar gains, people, equipment and stored energy can contribute with different signs. A cooling load can include sensible cooling and moisture-related latent effects. Peak demand and annual energy are different questions.

Equipment capacity is available output under stated conditions; it is not the same as the building’s required load or its electricity consumption. Distribution and control influence what reaches each zone. A nominally sufficient central output does not establish that every room receives the needed service, and a rating at one outdoor condition does not represent the whole operating year.

Heating COP describes a specified useful output

For a steady supplied heat-pump example, 1.5 kW electrical input plus 3.0 kW transferred from the environment gives 4.5 kW delivered heat. Heating coefficient of performance is 4.5/1.5=3. The numerator and denominator use compatible energy-rate units and a declared system boundary. The value is a constructed case, not a product specification.

In cooling mode, useful heat removal is the numerator of cooling COP. Rejected heat includes both the removed heat and the work input under the corresponding simple account. Pumps, fans, auxiliary heaters and distribution losses change a whole-system comparison if they lie outside the equipment-only boundary. State which of them are counted.

A seasonal total is a weighted account

Performance can change with source and delivery temperatures, part-load operation and auxiliary activity. A higher required delivery temperature can change the operating conditions rather than simply increasing the same output. Envelope and ventilation choices alter loads, so comparing equipment separately from those systems can conceal important interactions.

Calculate energy over matching intervals, using performance appropriate to each interval. Thermal storage shifts the timing of supply and demand but also has losses and capacity limits. Simultaneous heating and cooling in different zones may reflect legitimate needs or a control problem; investigate the required service and actual modes before assuming that one aggregate meter identifies the cause.

Use the actual interval performance in the supplied account

A separate original heating period needs 3 kW for 2 h at supplied COP 3, followed by 1 kW for 4 h at supplied COP 2. Delivered thermal energy is 3×2+1×4=10 kWh. Electrical energy is 6/3+4/2=4 kWh, excluding auxiliaries. The period COP based on the total is 10/4=2.5.

Applying COP 3 to the entire 10 kWh would predict 3.33 kWh and miss the changed second interval. If an additional fan used 0.1 kW throughout all 6 h, total purchased energy under an expanded boundary would be 4.6 kWh. These examples demonstrate accounting and boundaries; they do not select equipment, temperatures or an operating strategy.

Try the reasoning

1. Why can heating COP exceed one?

   Show the answer and reasoning

   Delivered heat includes energy transferred from the environment as well as the supplied work or electrical input.

2. What is the period COP for the two supplied intervals?

   Show the answer and reasoning

   Total delivered thermal energy 10 kWh divided by electrical energy 4 kWh gives 2.5 under the stated exclusions.

3. Does a central heating output prove every occupied zone is comfortable?

   Show the answer and reasoning

   No. Distribution, controls, envelope effects and local conditions determine the service experienced in each zone.

What to carry forward

Compare equal thermal service over the same period with an explicit energy boundary and condition-dependent performance.