EER and SEER
EER and SEER are the cooling counterparts of COP and SCOP. COP is the heating version: heat delivered per unit of electricity. In summer the machine works the other way round and moves heat out of the house. EER and SEER say how much leaves for each unit of electricity you pay for.
EER: cooling efficiency at one operating point
The energy efficiency ratio (EER) is the cooling capacity (how much heat the machine can remove) divided by the electrical power it draws, in the same units. An EER of 5 means 1 kWh of electricity removes 5 kWh of heat from the water or air being cooled.
Like COP, it is only valid at a stated test point. EN 14511, the standard for rating air conditioners and heat pumps, defines the conditions. The rating pairs an outdoor air temperature with a chilled-water temperature, the temperature of the water the machine sends to the cooling floor or to the room units. A35/W18 means 35 °C outdoor air and water leaving at 18 °C. A35/W7 means 35 °C outdoor air and water leaving at 7 °C.
The two water temperatures reflect two kinds of room units. A fan coil blows room air over a cold-water coil and needs colder water. A cooling floor works with water that is only moderately cool. European ecodesign rules rate comfort chillers that feed fan coils at 12/7 °C (water returning at 12 °C, leaving at 7 °C) and those that feed cooling floors or chilled beams (cooling panels in the ceiling) at 23/18 °C. The same machine has a much better EER when it only has to chill water to 18 °C. It is the same idea as in heating: the smaller the temperature gap between the cold side and the hot side, the less electricity the compressor needs.
SEER: efficiency over a cooling season
The seasonal energy efficiency ratio (SEER) is the cooling demand over a season divided by the electricity used to meet it. EN 14825 sets the calculation. It weights performance at several part-load conditions (a machine often runs below its full output) by how often each outdoor temperature occurs in a reference climate, a standard pattern of temperatures. That rewards units that work well at partial load. Like SCOP, it compares products under identical rules and does not forecast the cooling bill of your house.
How the model handles cooling
The wizard offers three ways to cool, and all three are modelled in EnergyPlus, the building simulation program the model runs on. In all three, cooling starts when a zone’s temperature rises above the cooling setpoint, the highest indoor temperature you ask for (24 °C by default). A zone is a part of the house the model treats as one block of air, usually one floor.
Floor cooling
The heat pump runs in reverse and sends chilled water through the same floor circuits that heat the house. The water is supplied at 18 °C. Floor cooling needs underfloor heating, because it runs through the same floor circuit, so the wizard does not offer it with radiators. For air-source units, the model uses the manufacturer’s published cooling capacity and EER at 18 °C water for each of six size classes, at seven outdoor temperatures from 20 to 45 °C. At 35 °C outdoors the EER runs from 3.7 to 4.7 across the classes. The values come from a manufacturer datasheet for one range of units, and none is estimated. Together the points make up the machine’s performance curve: how its efficiency changes with the outdoor temperature. For a size 10 unit the EER falls from 8.4 at 20 °C outdoors to 3.2 at 45 °C. Size is the obvious difference between a 16 kW unit and a 10 kW one. The curve is the less visible one.
Ground-source floor cooling works differently: it is passive. The compressor stays off, and the floor water gives its heat to the buried loop through a heat exchanger, so only the pumps use electricity. How much cooling the ground can deliver is calculated from the borehole field, so a short or small field delivers less of the cooling the house asks for.
Floor cooling with air conditioning backup
The floor works first. Air conditioning only takes the part of the load that the floor cannot deliver. That includes hours when the condensation limit shuts the floor circuit off. It is the safety rule that stops the floor getting cold enough to sweat.
Air conditioning only
A multi-split system: one shared outdoor unit and one indoor unit per cooled zone. Its capacity is sized from the house’s design cooling load, and the equipment step shows the sized value. The unit comes from one manufacturer’s published range, shown without the brand, and its rated EER is that unit’s own: rated cooling capacity divided by rated power input, from 3.3 to 4.3 across the range. Its efficiency changes with outdoor temperature along a generic performance curve, not the curve of that unit.
What the results show
The results report cooling delivered to the house in kWh and the electricity the cooling equipment used. The monthly electricity chart splits cooling electricity out. There is no separate seasonal cooling efficiency figure. If you want one, divide the cooling delivered by the cooling electricity for the year. That gives an effective annual EER for the whole run, which is close in spirit to SEER but not computed the EN 14825 way.
Limits of the model
- The air-source cooling data are published for one water temperature, 18 °C. The model joins the published outdoor points with straight lines.
- The chilled-water temperature is fixed, so the model does not show the efficiency gain you would get from running the floor circuit with warmer water.
- Part-load behaviour follows EnergyPlus’s heat pump model with a standard curve, not a manufacturer’s own control software.
- The air conditioning rating is that of a real unit, but the way its efficiency changes with outdoor temperature and load follows a standard curve set, not the unit’s own curves.
- The size classes are real models from one range, with no blending between neighbouring sizes.