Polyvalent heat pumps (PHPs) are soaring in popularity thanks to their ability to provide heating and cooling services simultaneously and independently, and not just seasonally (as is the case with traditional reversible heat pumps).
The rapidly growing interest in PHPs has prompted Rhoss to partner with the Polytechnic University of Turin in Italy to produce a pioneering paper entitled ‘Contemporary and unbalanced loads in buildings: new performance indicators’.
The paper – published by REHVA*, the Federation of European Heating, Ventilation and Air Conditioning Associations – aims to develop new key performance indicators (KPIs) to assess heating and cooling demands, and to quantify and ascribe value to the benefits that PHPs can offer.
In light of recent developments in control systems, it also examines the potential offered by coupling more units (including PHPs) with lower nominal capacities rather than oversizing single units to meet the highest load.
The paper says: “According to EN 14825… seasonal indexes are computed using linear loads and defining the number of hours of heating and cooling seasons and the reference temperature bands for their calculations, according to diverse climatic conditions (i.e., warmer, average, and colder climates).”
However, it adds, when estimating PHPs’ performances, challenges arise from this approach: “It is limiting to consider fixed temperature ranges for the loads definition, as well as to define two separate and independent heating and cooling seasons; indeed, using this approach, it is not possible to account for possible contemporary heating and cooling requests, or to consider the number of contemporaneity hours, and these aspects are the main advantages of PHPs.”
The methodology proposed in the Rhoss/Turin University paper comprises two main parts:
- Numerical experimentation to model the coupling between load profiles and units’ operational dynamics.
- Producing KPIs to define a set of metrics able to express the technical performances of the analysed technological solutions.
The work aims to develop new metrics to assess the performance of HVAC systems (both single- and multi-units) in the presence of contemporary and unbalanced heating and cooling loads in buildings.
Based on its newly developed KPIs, the paper allows the comparison of two configurations (PHP versus PHP and chiller). The integration of PHP and chiller, using units with lower nominal capacities, appears to be more beneficial in terms of the annual performance indicator as well as from financial and environmental standpoints.
Future development is planned to refine the numerical approach to test the defined KPIs with other HVAC configurations and diverse contemporary load profiles, and to enlarge the set of metrics (always aiming to assign value to the technologies’ ability to meet contemporary loads).
To download the paper, click here.
Rhoss is a supply partner of Klima-Therms: www.rhoss.com
* REHVA is an umbrella organization that represent over 120,000 HVAC designers, building services engineers, technicians, and experts across 26 European Countries.