Heat Pumps

Heat pumps have increasingly come into focus as one of the most sustainable heat generators — and (always) as cooling generators — because they use electricity as an energy source, which, if produced sustainably, can provide the required useful energy while reducing CO₂ emissions in energy concepts.

Sizing

A key advantage of the Building Design Days + Energy (BDD+E) method is that real measured efficiencies and part-load performance curves can be applied for generation components. These then lead, on an hourly basis, to seasonal performance factors and other derived values. Heat pumps in particular are very sensitive with regard to oversizing and part-load behavior.

Manufacturers of heat pumps usually provide the following product data: nominal capacity and SCOP.

• The specification of the nominal capacity of a heat pump corresponds exactly to a real measured efficiency (COP: coefficient of performance) at that specific operating point, provided that at that moment precisely this capacity is required.
• The seasonal coefficient of performance (SCOP), however, is determined based on an unclear scenario of a fictitious heating load profile in winter. This value is not useful for planning when it comes to selecting and sizing a specific heat pump.

To size heat pumps sustainably, a realistic heating demand is required. The Building Design Days + Energy method provides an hourly load profile of heating demand, which must be covered by a generator at each respective point in time. This makes it possible to take into account the generator’s real efficiencies under the hourly boundary conditions, thereby determining its operating behavior, including part-load performance, and obtaining full-load hours as a result.

For example, an air-to-water heat pump can draw the required hourly heating energy from the outdoor air temperature source to cover the hourly heating demand. Using the BDD+E method, this component can be sized and evaluated.

BDD+E as a Basis for Testing Procedures for Heat Pumps

With the BDD+E method, it is possible, for example, to demonstrate for a heat pump in a test building — with window area ratio, orientation, and construction type in the respective climate — which seasonal performance factor, part-load behavior, or full-load hours it will achieve as a result.

In addition, a planner can use project-specific inputs to perform a preliminary sizing and evaluate the involved generation components for a specific building project.