Heating and Cooling with Ground-Source Heat Pumps in Cold and Moderate Climates

Fundamentals and Basic Concepts

Vasile Minea

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000564327
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Heating and Cooling with Ground-Source Heat Pumps in Cold and Moderate Climates: Fundamentals and Basic Concepts covers fundamentals and design principles of vertical and horizontal indirect and direct expansion closed-loop, as well as ground and surface-water ground-source heat pump systems. It explains the thermodynamic aspects of mechanical and thermochemical compression cycles of geothermal heat pumps, and describes the energetic, economic, and environmental aspects associated with the use of ground-source heat pump systems for heating and cooling residential and commercial/institutional buildings in moderate and cold climates.

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• Based on the author's more than 30 years of technical experience

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• Focuses on ground-source heat pump technologies that can be successfully applied in moderate and cold climates

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• Discusses technical aspects as well as the most common and uncommon application fields of basic system configurations

This work is aimed at designers of HVAC systems, as well as geological, mechanical, and chemical engineers implementing environmentally-friendly heating and cooling technologies for buildings.

1 Introduction

DOI: 10.1201/9781003032540-1

Volume 1 of this book focuses on fundamentals, basic concepts, and design principles of vertical and horizontal indirect (secondary fluid) and direct (mono-fluid) expansion closed-loop, and groundwater and surface water very low-temperature (low-enthalpy) ground-source heat pump systems. It details some thermodynamic aspects of mechanical vapor compression geothermal heat pumps, as well as technical, energetic, economic, commercial, and environmental information associated with the use of ground-source heat pump systems for heating and cooling residential, commercial/institutional, and equivalent industrial buildings in moderate and cold climates.

Chapter 2 first summarily presents some information related to outdoor and indoor design temperatures as well as principles of heating and cooling loads for both residential and commercial/institutional buildings in cold and moderate climates. Second, the most commonly used software tools in industry and academia for whole building simulation including or not means to simulate the major ground-source heat pump systems and their sub-systems are summarized.

Chapter 3 presents several types of HVAC systems for both residential and commercial/institutional buildings. The main components of each selected concept are identified as well as their principal advantages and drawbacks.

Chapter 4 defines the deep (high- and moderate-temperature) and shallow (low- and very-low temperature) geothermal energy resources; provides short information about their origins, depths, and temperatures; as well as on their usages and thermal conversion technologies.

Chapter 5 presents the main types of ground/soils and shortly describes some of their thermos-physical properties of interest for ground-source heat pump systems.

Chapter 6 succinctly presents some laboratory as well as in-field currently used methods to evaluate the ground/soil/rocks effective (average) thermal conductivity. Details are included on typical mobile apparatus, and some testing methods.

Chapter 7 refers to the classification of ground-source heat pump systems currently used in cold and moderate climates according to their application fields and heat/sink energy sources.

Chapter 8 first presents the basic thermodynamic parameters of real subcritical mechanical vapor compression geothermal heat pump, and most-used diagrams and refrigerants. Second, the thermodynamic cycles of typical brine-to-air geothermal heat pumps with vertical closed-loop (indirect, secondary fluid) ground-coupled heat exchangers operating in heating and cooling modes, are described. Finally, some means to express the energy and exergy efficiencies of geothermal heat pumps are detailed.

Chapter 9 presents some aspects related to typical construction of refrigerant-to-air condensers of geothermal heat pumps, and some basic relations (as overall heat transfer coefficients and heat transfer rates), required for their thermal design.

Chapter 10 refers to some construction (as tube and fins materials, refrigerant and air flow distribution, and condense draining) of conventional finned-tube air-to-refrigerant evaporators for geothermal heat pumps, and heat transfer (as thermal resistance, overall heat transfer coefficient, heat transfer rate, and heat transfer surface) aspects.

Chapter 11 first describes the conventional distributed and central geothermal heat pump systems usually applied in large-scale commercial and institutional buildings. It provides information about current materials for piping, as well as some basic notions concerning brine and water pumping.

Chapter 12 presents the basic configurations and operating modes of residential and commercial/institutional vertical closed-loop (indirect, secondary fluid) ground-source heat pump systems, as well as some fundamental elements of heat transfer inside and outside the boreholes.

Chapter 13 describes the heat transfer inside and outside borehole heat exchangers provided with single U-shaped vertical tubes. Also summarized are some aspects of analytical (as infinite line- and cylindrical-source) and numerical (as long- and short-term) analyzing methods.

Chapter 14 summarizes several characteristics of closed-loop (indirect, secondary fluid) horizontal ground-source heat pump systems applied to residential and non-residential buildings, as the complex influences heat and mass transfer with the ambient air, heat transfer around buried ground-coupled heat exchangers, as well as flow regimes and convective heat transfer of thermal carrier fluids inside horizontally buried pipes.

Chapter 15 presents the basic concepts and their operating principles, some performance indicators and rating conditions, refrigerant flow patterns, pressure drops and heat transfer (vaporization and condensation) principles, as well as the main advantages and limitations of both horizontal and vertical closed-loop, direct expansion (mono-fluid) ground-source heat pump systems.

Chapter 16 first presents the basic configurations as well as the operating principles of closed-loop vertical thermos-syphon ground-source heat pump systems, and the characteristics of the most used working fluids. Second, the density, pressure, temperature, and velocity profiles are identified, as well as the heat transfer mechanisms and the thermal resistance. Finally, some advantages and drawbacks of these systems, and future R&D needs are summarized.

Chapter 17 first classifies the open-loop groundwater systems, and then presents a number of the most relevant properties of aquifers and the potential problems that may impact the safe operation of geothermal heat pumps. Some advantages and limitations of open-loop groundwater heat pump systems are finally summarized.

Chapter 18 presents the basic configurations of open-loop, dual, and multiple-well groundwater heat pump systems for residential and commercial/institutional buildings. The main components of production and return wells are described, and the characteristics of groundwater submersible pumps.

Chapter 19 refers to basic concepts and configurations of open-loop single-well (standing column) groundwater heat pump systems that can be applied to residential and commercial/institutional buildings. Some characteristics of groundwater flow and heat transfer outside and inside standing column wells are presented.

Chapter 20 first presents the basic concepts of open- and closed-loop surface water ground-source heat pump systems for residential and commercial/institutional buildings. The main physical properties of stationary surface water and stratification/mixing/turnover phenomenon are then shortly described. Finally, the heat transfer and energy balance at the surface bodies are detailed.

Chapter 21 summarizes some of technical, energetic, operational, economic, and environmental advantages and limitations of ground-source heat pump systems.

Chapter 22 first describes the actual context and targets of heat pumping technology, and then summarizes some of future R&D needs, aiming to improve the energy and economic efficiency of the technology in order to respond to global requirements of the humanity.

2 Outlook for Building Heating and Cooling Loads, and Simulation Tools

DOI: 10.1201/9781003032540-2

2.1 Introduction

To accurately design and size the ground-source heat pump systems in any geographical location, it should first determine the buildings’ heating and cooling loads (i.e., average amounts of energies that must be added to or removed from spaces during each month of the year) to maintain the indoor temperatures and relative humidity at the design values.

Building heating and cooling loads significantly affect the size of ground-coupled heat exchangers, piping, air handlers, and distribution ductwork (Bose et al. 1985; DOE 1995; ASHRAE 2011).

For both residential and commercial/institutional buildings, the calculation of heating and cooling loads requires the knowledge of elements as the followings: (i) building type, size, and space usage; (ii) outdoor and indoor thermal conditions; (iii) occupancy (number of people) and activity of space occupants; and (iii) characteristics of the equipment emitting heat and/or moisture in the conditioned spaces.

The main contributors to building heating and cooling energy requirements are: (i) heat transmission through building structures; (ii) un-controlled air infiltration; (iii) controlled fresh air ventilation; (iv) solar radiation; (v) lights; (vi) electrical appliances and motors; and (vii) materials entering/leaving the buildings.

2.2 Outdoor and Indoor Design Conditions

Outdoor design conditions for building annual heating and cooling load calculations in the coldest and hottest months of the year should be selected according to local climate data and code requirements.

For most North American locations, for example, the winter (December, January, and February, i.e., a total of 2,160 hours) and summer (June through September, i.e., a total of 2,928 hours) design temperatures usually selected are the outdoor dry-bulb air temperatures that exceeded 97.5% and 2.5% of the total hours during the winter and summer months, respectively. The mean coincident wet-bulb and dew-point temperatures are tabulated along the dry-bulb design temperature values, and, generally, the most unfavorable combination of outdoor air temperatures and relative humidity in winter, assumed at 70–80% for most locations), and wind mean velocities occurring at the specific dry-bulb temperatures is commonly used (ASHRAE 2011). Common indoor conditions for heating and cooling are 20°C dry-bulb temperature and 30% relative humidity, and 24°C dry-bulb temperature and 50–65% relative humidity, respectively.

The concept of ‘’indoor thermal comfort’’ involves the interaction of many factors, generally pertaining to sedentary physical activity levels of healthy adults at atmospheric pressure equivalent to altitudes up to 3,000 m and for periods not less than 15 minutes. According to ANSI/ASHRAE Comfort Standard 55 (2010), in spaces where the occupants have activity levels that result in metabolic rates between 1.0 and 1.3 met. Met the energy produced per unit surface area (about 1.8 m²) inside the body due to metabolic activity of an average person seated at rest (e.g., 58.2 W/m²) and where clothing provides between 0.5 and 1.0 clo (where clo is an unit used to express the thermal insulation provided by clothing ensembles; 1 clo = 0.155 °C∙m²/W of thermal insulation).

In Figure 2.1, two comfort zones are shown: one for 0.5 clo (when the outdoor environment is warm) and one for 1.0 clo (when the outdoor environment is cool) of clothing insulation, respectively. It can be seen that: (i) the comfort zone moves left with higher clothing, higher metabolic rate, and higher radiant temperature; and (ii) the comfort zone moves right with lower clothing, lower metabolic rate, and lower radiant temperature. The graph shown in Figure 2.1 applies to operative temperatures only, defined as the uniform temperatures of imaginary black enclosures in which the occupants would exchange the same amount of heat by radiation plus convection as in actual non-uniform environments. It represents the range of operative temperatures for 80% occupant acceptability. In other words, this is based on a 10% dissatisfaction criterion for general (whole body) thermal comfort, plus an additional 10% dissatisfaction that may occur on average from local (partial body) thermal discomfort.

Figure 2.1 Ranges of operative temperature and absolute humidity for comfort zones.

The operational temperature, a simplified measure of human thermal comfort derived from air dry-bulb temperature, mean radiant temperature, and speed, is defined as follows:

$OT=\frac{{\overline{T}}_{rad}+{\overline{T}}_{air}\sqrt{10\ast w_{air}}}{1+\sqrt{10\ast w_{air}}}$(2.1)

where

$\mathrm{OT}$ is the operative temperature (°C)

${\overline{T}}_{rad}$ is the mean radiant temperature (°C)

${\overline{T}}_{air}$ is the mean dry-bulb air temperature (°C)

$w_{air}$ is the air velocity (m/s)

The operative temperature can be also expressed as follows:

$OT=\frac{h_{rad}\cdot {\overline{T}}_{rad}+h_{conv}\cdot {\overline{T}}_{air}}{h_{rad}+h_{conv}}$(2.2)

where

${\mathrm{h}}_{\mathrm{rad}}$ is the radiative heat transf...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• Biography
• Chapter 1 Introduction
• Chapter 2 Outlook for Building Heating and Cooling Loads, and Simulation Tools
• Chapter 3 Conventional Building HVAC Systems
• Chapter 4 Geothermal Energy Resources
• Chapter 5 Ground/Soil Types and Thermo-Physical Properties
• Chapter 6 Determination of Ground/Soil Effective Thermal Conductivity
• Chapter 7 Classifications of Ground-Source Heat Pump Systems
• Chapter 8 Geothermal Heat Pumps
• Chapter 9 Refrigerant-to-Air Condensers
• Chapter 10 Air-to-Refrigerant Evaporators
• Chapter 11 Closed-Loop (Indirect, Secondary Fluid) Ground-Source Heat Pump Systems
• Chapter 12 Vertical Closed-Loop (Indirect, Secondary Fluid) Ground-Source Heat Pump Systems
• Chapter 13 Heat Transfer
• Chapter 14 Horizontal Closed-Loop (Indirect, Secondary Fluid) Ground-Source Heat Pump Systems
• Chapter 15 Closed-Loop Direct Expansion (Mono-Fluid) Ground-Source Heat Pump Systems
• Chapter 16 Closed-Loop Vertical Thermo-Syphon Ground-Source Heat Pump Systems
• Chapter 17 Open-Loop Groundwater Heat Pump Systems
• Chapter 18 Open-Loop, and Dual- and Multiple-Well Groundwater Heat Pump Systems
• Chapter 19 Open-Loop Single-Well (Standing Column) Groundwater Heat Pump Systems
• Chapter 20 Surface Water Ground-Source Heat Pump Systems
• Chapter 21 Advantages and Limitations of Ground-Source Heat Pump Systems
• Chapter 22 Future R&D Requirements
• Index