95522 - PROGETTAZIONE DI IMPIANTI A POMPA DI CALORE M

Learning outcomes

At the end of the course, the student is skilled in the use of the main procedures for the design of air conditioning systems based on air and water heat pumps and on the sizing of the fields of geothermal probes, vertical and horizontal, to be combined with heat pumps. In particular, the student is able to: - know the technical characteristics of the main types of heat pumps available on the market ; - size air conditioning system based on air and water heat pumps; - evaluate the impact of the geothermal borehole fields on the system energy performance; - perform assessments on heat pump systems based on concepts of economy, sustainability and energy efficiency ; - carry out dynamic simulations of heat pump systems using commercial software.

Course contents

First Part - Basic concepts and air-source heat pumps

Definitions and regulatory framework. Current diffusion of heat pumps in Europe. Regulatory framework on heat pumps at European, Italian and regional level. Legislative Decree 8 November 2021, n.199. Definitions of energy from renewable sources, from environment and geothermal energy. Obligations on the use of renewable energy. DGR 1261 Emilia-Romagna. UNI/TS 11300-4. Conversion factors of energy vectors. Numerical example on the calculation of the primary energy need and the share of renewable energy.

Recalls and heat pump classifications. Heat pumps and chillers. Heat reservoirs and thermodynamic constraints. Reversibility of the machine. Energy Efficiency Ratio (EER) and Coefficient Of Performance (COP). Example. Heat pumps classification based on the cold/hot reservoirs. Efficiency vs availability. Heat pumps classification based on the operating principle and on the thermodynamic cycle.

Electric vapor compression Heat Pumps (EHP). Operation scheme. Cycle on (p,h) diagram. Ideal cycle and real cycle. Vapor compression cycle components: compressor, condenser, evaporator, lamination valve. Refrigerant fluids. Energy balance of a heat pump in heating/cooling operation. Numerical example. Parameters affecting a heat pump efficiency.

Gas Heat Pumps (GHP) and Absorption Heat Pumps (AHP). GHP plant scheme and operating principles. Mechanical efficiency and thermal efficiency. Fuel Utilization Coefficient and Primary Energy Ratio (PER). Numerical example. Comparison of performance parameters and energy flows between GHPs and EHPs. Advantages and disadvantages of GHPs. AHP plant scheme and operating principles. Internal cycle and external cycle. Cycles on (p,T) diagram. Energy analysis and Gas Utilization Efficiency (GUE). Advantages and disadvantages of AHPs.

Heat pump characterization. Characterization by second principle efficiency. Characterization by interpolation of manufacturer data at full capacity. Data required by static simulation software. Example.

Coupling with building and heat pump sizing. Building energy signature and heat pump characteristic curve. Balance point and bivalent temperature, zero-load temperature, cut-off temperature and TOL. On-off/multi-compressor/inverter-driven heat pumps. Load ratio and heat pump performance at partial loads. UNI EN 14825 and Part Load Ratio (PLR). Heat pump sizing in monovalent/bivalent-monoenergetic/bivalent-bienergetic operation. Numerical examples.

Calculation of seasonal and annual performance factors. Seasonal Coefficient Of Performance (SCOP) and Seasonal Energy Efficiency Ratio (SEER). Calculation on monthly basis/bin method. Calculation of the parameters SCOPnet, SCOPon and Primary Energy Ratio (PER). Sizing rules and effects on SCOP. Annual Performance Factor (APF) of a reversible heat pump. Numerical examples.

HVAC plant with heat pump. Heat pumps and terminal units. Thermal energy storage and temperature variations. Defrosting problem in air-source heat pumps. High temperature heat pumps. Multifunction chillers and total heat recovery. Examples. Dynamic energy simulations of heat pump systems.

Second Part - Geothermal heat pumps and energy-economic evaluations

Definitions and classification of geothermal heat pumps. Geothermal reservoir. Classification of geothermal sources. High and medium enthalpy geothermal sources. ASHRAE classification of geothermal heat pumps: Ground Coupled Heat Pumps (GCHPs), Ground Water Heat Pumps (GWHPs), Surface Water Heat Pumps (SWHPs). Vertical GCHPs: characteristics of vertical heat exchangers (boreholes). Horizontal GCHPs: types of horizontal heat exchangers and arrangements.

Closed circuit Surface Water Heat Pumps (SWHPs). Description of the heat exchangers. Calculation of internal and external convection coefficients. Sizing of heat exchangers. Calculation of head losses. Examples of heat exchangers sizing.

Borehole thermal resistance and Thermal Response Test (TRT). Definition of the borehole thermal resistance. Approximate expressions. Evaluation by finite element simulation. Effective thermal resistance and Hellström analytical method. Aims and phases of a TRT. Test circuit recommended by ASHRAE. Determination of the undisturbed ground temperature. Determination of the ground thermal conductivity and of the borehole thermal resistance, or of the ground thermal conductivity and diffusivity. Geological and hydrogeological characteristics of the region Emilia-Romagna. Example of stratigraphy detected during a borehole drilling.

ASHRAE-UNI sizing method of borefields. Total boreholes length for cooling and heating. Determination of the ground thermal resistances for annual, monthly, daily impulses, through g-factor. Penalty factors for thermal short-circuit and interference between boreholes. Example of borefield sizing through ASHRAE-UNI method.

UNI sizing method for horizontal ground heat exchangers. Expressions for the total pipe length, for heating and cooling. Thermal power on the ground side and monthly partial load factors. Evaluation of the pipe linear thermal resistance. Calculation of the ground thermal resistance and temperature at the pipe average depth. Example of dimensioning of a horizontal ground heat exchanger with UNI method.

Borefield sizing through the g-function method. Limitations of the ASHRAE sizing method. Definition of g-function. Finite Line Source (FLS) and Finite Cylindrical Source (FCS) methods. Numerical/analytical evaluation of g-functions with FLS scheme. Determination of the dimensionless temperature averaged over the borehole length caused by a time-varying thermal load. Determination of the borefield g-function. Numerical example.

Long-term sustainability of borefields. Problem for a square field with only winter thermal loads, in the absence of groundwater movement. Effect of groundwater movement on the apparent thermal conductivity of the ground and on the long-term sustainability of large borefields.

Energy and economic aspects. Primary Energy Saving. Energy convenience of electric/gas/absorption heat pumps. Environmental impact of heat pumps. Economic savings due to electric/gas/absorption heat pumps. Numerical examples. Economic payback time. Example of payback time calculation: replacement of a gas boiler with a ground-coupled heat pump system. Economic incentives for heat pumps in Italy.

Readings/Bibliography

Lecture notes provided by the teacher available on https://virtuale.unibo.it/ (in Italian).

For any further information (not mandatory for the exam):

- R. Lazzarin, F. Busato, F. Minchio, M. Noro, Sorgenti termiche delle pompe di calore – Aspetti tecnici, economici e normativi, Collana Tecnica AiCARR, Editoriale Delfino, Milano, 2012 (in Italian).

- ASHRAE 2015 Handbook, HVAC Applications, Chapter 34.

- S. Kavanaugh, K. Rafferty, Geothermal Heating and Cooling - Design of Ground-Source Heat Pump Systems, ASHRAE, Atlanta, 2014.

Teaching methods

The course includes theoretical lessons with application examples, carried out in Italian in classroom (in presence classes). Slides, blackboard/virtual whiteboard and simulation software will be used.

A visit is planned to the Applied Thermal Engineering Laboratory of the Department of Industrial Engineering (via Terracini 34, Bologna), where a climatic chamber for heat pumps testing and a borefield equipped with optical fiber have been built.

Lectures by experts from industry are included.

In consideration of the types of activities and teaching methods adopted, the frequency of this course requires all students to pass modules 1, 2 (e-learning) and 3 on safety in working areas. Information available in the specific section of the degree program website.

Assessment methods

The notion acquired are assessed through an oral exam, which includes two questions on two distinct topics: one on the first part of the course and one on the second part (each of equal weight for the final grade formulation). Grades:

Very limited preparation and analytical skills emerging only with the teacher help, correct language: 18-19;

Very limited preparation and capacity for autonomous analysis only on purely executive matters, correct language: 20-24;

Extensive preparation, ability to make autonomous choices of critical analysis, specific terminology: 25-29;

Exhaustive preparation, ability to make autonomous choices of critical analysis and connection, specific terminology and argumentation skills: 30-30L.

A scientific calculator is required.

Students can find the list of exam sessions on the website https://almaesami.unibo.it/

Eligible students (out-of-course and laureandi) can contact the teacher to fix ad-hoc exam sessions.

Teaching tools

PC-assisted presentations, blackboard/virtual whiteboard, simulation software (Comsol, Matlab-Simulink, Trnsys), experimental set-up of the Applied Thermal Engineering Laboratory.

Material available on https://virtuale.unibo.it/

Office hours

See the website of Claudia Naldi