# Application of a New Dynamic Heating System Model Using a Range of Common Control Strategies

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## Abstract

**:**

## 1. Introduction

## 2. Modelling of HVAC Systems and Controls

- (1)
- Develop robust circuit control strategies with multi-zone functionality commonly adopted in current design practice for secondary system side and advanced system control strategies;
- (2)
- Embed primary and secondary HVAC systems and component models within parent code; and
- (3)
- Test and demonstrate the capabilities of the primary and secondary HVAC systems adopting a wide range of control strategies and primary plant system configurations.

## 3. Development of HVAC Systems and Controls

- (1)
- Constant Temperature, Varying Flow rate (1CTVF), typically used in zone feedback control;
- (2)
- Varying Temperature, Constant Flow rate (2VTCF), typically used in weather-compensated control;
- (3)
- Varying Temperature, Varying Flow rate (3VTVF), typically used when both of the above methods are combined; and
- (4)
- Constant Temperature, Constant Flow rate (4CTCF), typically used in simple thermostatic (i.e., “on-off”) control.

#### 3.1. Variable Flow Rate

#### 3.2. Variable Temperature

#### 3.3. Constant Temperature and/or Constant Flow Rate

#### 3.4. Assumptions for Primary HVAC Systems

- All emitter systems are connected to a single main circuit on the secondary side;
- A maximum of three units of primary plant have been specified for each of the heating systems tested and compared in this research;
- Pressure loss effects in pipe fittings and plant are neglected;
- The schedule controller is designed to offer the minimum number of primary plant (e.g., boilers) to satisfy load requirements;
- Loads are shared equally between the online primary plant;
- Flow rate entering the primary plant is constant; and
- Required flow water temperature by the secondary systems is constantly met.

#### 3.5. Modelling of Primary HVAC Systems

#### 3.5.1. Step 1: Low Loss Header Node

#### **(a) Weighted average return water temperature across all zones**

#### **(b) Sum of total mass flow rate of all zones**

#### 3.5.2. Step 2: Controller Node

#### Primary Plant Systems Configurations

- (1)
- Conventional system(s) only;
- (2)
- Renewables system(s) only; and
- (3)
- Hybrid system(s).

#### 3.5.3. Step 3: Balance Pipe Node

#### 3.6. Development of Primary Plant Models

- Conventional gas-fired boiler;
- Biomass boilers; and
- Heat pumps.

#### 3.6.1. Development of Conventional and Biomass Boiler Models

#### 3.6.2. Development of Heat Pump Models

## 4. Testing/Debugging of Primary Plant Models

#### 4.1. Test Case Building Model

^{2}has been adopted [22]. The models developed for this research are tested against EnergyPlus (version 7.2.0.006, U.S. Department of Energy, Washington D.C., U.S.) and IES VE (version 6.4.0.10, Integrated Environmental Solutions, Glasgow, U.K.), two building energy modelling tools widely used in both academia and industry. Inter-model comparison [23] is an accepted tool to verify simulation software results.

#### 4.2. Thermal Comfort

#### 4.3. Energy Consumption by Primary Plant

^{2}fuel and 32 kWh/m

^{2}electricity for typical practice, and 113 kWh/m

^{2}fuel and 22 kWh/m

^{2}electricity for good practice [26] over the treated area. Results in Table 4 show that the energy predictions made by the detailed HVAC module developed for this research are within limits of good and typical practices for the test scenarios, as recommended by CIBSE [26].

## 5. Conclusions

## 6. Limitations

## 7. Future Work

- Extend the control options at primary system level to include advance control options;
- Extend the library of components to encompass a larger variety of primary system types;
- Conduct empirical validation of the new program; and
- Modify the detailed HVAC module to incorporate sophisticated features in C++ for better memory management to further improve computational efficiency.

## Acknowledgments

## Author Contributions

## List of Symbols

$\left(z\right)$ | zone index |

$m$ | emitter mass flow rate (kg/s) |

${m}_{\text{Des}}$ | emitter mass flow rate at design (kg/s) |

${m}_{\mathrm{r}}$ | emitter return mass flow rate (kg/s) |

${m}_{\text{Ret}}$ | sum of mass flow rate (kg/s) |

$\text{ProportionalBand}$ | proportional band (Kelvin) |

${T}_{\text{ao}\_curr}$ | external dry bulb temperature at current time-step (°C) |

${T}_{\text{aoDes}}$ | external dry bulb temperature at design (°C) |

${T}_{\text{ai}}$ | internal air temperature (°C) |

${T}_{BP\left(z\right)}$ | balance point temperature (°C) |

${T}_{\mathrm{f}\_\text{curr}}$ | emitter flow water temperature at current time-step (°C) |

${T}_{\text{fDes}}$ | emitter flow water temperature at design (°C) |

${T}_{\text{fMin}}$ | emitter flow water temperature at minimum (°C) |

${T}_{\mathrm{r}}$ | emitter return water temperature (°C) |

${T}_{wrt}$ | emitter weighted return water temperature (°C) |

Z | total number of zones |

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**Table 1.**Example fitted coefficients for heat pump models [20].

AQUACIAT 2—240V | AQUACIAT2—900Z | AQUACIAT2—1200Z | ||||
---|---|---|---|---|---|---|

Capacity 63.7 kW | Capacity 213 kW | Capacity 286.7 kW | ||||

Condenser Coeff. | Compressor Coeff. | Condenser Coeff. | Compressor Coeff. | Condenser Coeff. | Compressor Coeff. | |

A | 60.97871667 | 11.49897395 | 187.3930858 | 6.415520459 | 254.1593333 | 61.24019048 |

B | 1.762304792 | 0.025778046 | 5.259652792 | 0.573394462 | 7.660742857 | 0.124542857 |

C | 0.009100576 | 0.000567554 | 0.021463022 | 0.005951499 | 0.029885714 | −0.006714286 |

D | −0.117275216 | 0.032945715 | −0.401422693 | 2.313005785 | −0.645866667 | 0.393047619 |

E | −0.001228087 | 0.005115675 | 0.005864981 | −0.015202763 | 0.008857143 | 0.020666667 |

F | −0.01179369 | −0.001005455 | −0.021895121 | −0.009212684 | −0.03952 | 0.010514286 |

Name | External Wall | (mm) | Flat Roof | (mm) | Partitions | (mm) | Ceiling Floor | (mm) | Ground Floor | (mm) |
---|---|---|---|---|---|---|---|---|---|---|

Outside Layer | Brickwork | 100 | Stone Chippings | 10 | Plaster | 13 | Synthetic Carpet | 10 | London Clay | 500 |

Layer 2 | Dense EPS Slab Insulation | 58 | Bitumen | 5 | Brickwork | 105 | Cast Concrete | 100 | Brickwork | 250 |

Layer 3 | Concrete block | 100 | Cast Concrete | 150 | Plaster | 13 | – | – | Cast Concrete | 100 |

Layer 4 | Gypsum Plastering | 13 | Glass Wool | 134 | – | – | – | – | Dense EPS Slab Insulation | 6.35 |

Layer 5 | – | – | Ceiling Tiles | 10 | – | – | – | – | Chipboard | 2.5 |

Types of Emitter: | |||

1 | Underfloor Heating | UFH | |

2 | Radiators | Rads | |

Types of Circuit Control Strategy: | |||

1 | Constant Temperature, Variable Flow rate | 1CTVF | |

2 | Variable Temperature, Constant Flow rate | 2VTCF | |

3 | Variable Temperature, Variable Flow rate | 3VTVF | |

4 | Constant Temperature, Constant Flow rate | 4CTCF | |

Types of Primary System Configurations: | |||

1 | Conventional | 2 × 300 kW Conventional Boiler | CBLR |

2 | Conventional | 3 × 200 kW Conventional Boiler | CBLR |

3 | Renewables | 2 × 300 kW Biomass Boiler | BMB |

4 | Renewables | 3 × 200 kW Biomass Boiler | BMB |

5 | Renewables | 2 × 300 kW Heat Pump | HP |

6 | Renewables | 3 × 200 kW Heat Pump | HP |

7 | Hybrid | 1 × 300 kW Biomass Boiler | BMB |

1 × 300 kW Conventional Boiler | CBLR | ||

8 | Hybrid | 1 × 300 kW Heat Pump | HP |

1 × 300 kW Conventional Boiler | CBLR |

Type | System Configuration | Energy Consumption | Underfloor Heating | Radiator | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|

1CTVF | 2VTCF | 3VTVF | 4CTCF | 1CTVF | 2VTCF | 3VTVF | 4CTCF | ||||

1 | Conventional | 2 × 300 kW Conventional Boiler | GAS kWh/m^{2} | 174.52 | 94.98 | 113.85 | 231.15 | 123.30 | 119.60 | 186.50 | 236.17 |

2 | Conventional | 3 × 200 kW Conventional Boiler | GAS kWh/m^{2} | 177.80 | 101.97 | 120.73 | 231.67 | 121.95 | 117.54 | 186.88 | 237.51 |

3 | Renewables | 2 × 300 kW Biomass Boiler | GAS kWh/m^{2} | 215.93 | 121.18 | 144.09 | 279.48 | 149.47 | 149.99 | 231.73 | 285.01 |

4 | Renewables | 3 × 200 kW Biomass Boiler | GAS kWh/m^{2} | 218.84 | 128.76 | 152.20 | 280.80 | 148.50 | 146.11 | 231.04 | 287.36 |

5 | Renewables | 2 × 300 kW Heat Pump | ELECT kWh/m^{2} | 76.23 | 54.91 | 55.20 | 81.97 | 138.20 | 83.80 | 113.39 | 163.95 |

6 | Renewables | 3 × 200 kW Heat Pump | ELECT kWh/m^{2} | 74.05 | 47.44 | 49.66 | 84.27 | 73.41 | 61.93 | 92.09 | 108.77 |

7 | Hybrid | 1 × 300 kW Biomass Boiler, 1 × 300 kW Conventional Boiler | GAS kWh/m^{2} | 184.78 | 93.84 | 111.53 | 255.29 | 104.20 | 95.07 | 194.82 | 259.61 |

8 | Hybrid | 1 × 300 kW Heat Pump | ELECT kWh/m^{2} | 45.40 | 38.73 | 37.65 | 41.74 | 96.80 | 61.59 | 62.09 | 82.36 |

1 × 300 kW Conventional Boiler | GAS kWh/m^{2} | 68.31 | 18.70 | 28.99 | 113.83 | 9.54 | 6.67 | 54.30 | 117.73 |

Advantages | Disadvantages | |
---|---|---|

1CTVF—Constant Temperature, Variable Flow | Commonly and widely adopted by radiators | – |

2CTVF—Variable Temperature, Constant Flow | Inexpensive method of control Commonly and widely implemented | Ignorant of zone internal temperature Increased risk of overheating Zones must be zonal controlled according to orientation/facing |

3VTVF—Variable Temperature, Variable Flow | Takes into account of zone internal temperatures | Increased cost to implement control for both temperature and flow rate in terms of mechanically and control wiring |

4CTCF—Constant Temperature, Constant Flow | Inexpensive method of control | Requires more energy (especially for fast acting radiators) as it toggles between fully on and fully off |

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**MDPI and ACS Style**

Fong, J.; Edge, J.; Underwood, C.; Tindale, A.; Potter, S.; Du, H. Application of a New Dynamic Heating System Model Using a Range of Common Control Strategies. *Buildings* **2016**, *6*, 23.
https://doi.org/10.3390/buildings6020023

**AMA Style**

Fong J, Edge J, Underwood C, Tindale A, Potter S, Du H. Application of a New Dynamic Heating System Model Using a Range of Common Control Strategies. *Buildings*. 2016; 6(2):23.
https://doi.org/10.3390/buildings6020023

**Chicago/Turabian Style**

Fong, Joshua, Jerry Edge, Chris Underwood, Andy Tindale, Steve Potter, and Hu Du. 2016. "Application of a New Dynamic Heating System Model Using a Range of Common Control Strategies" *Buildings* 6, no. 2: 23.
https://doi.org/10.3390/buildings6020023