HVAC Design | Full Analysis of Principles, Design, Selection, Construction, and Debugging of Air Source Heat Pumps!

1. HVAC Design | Full Analysis of Principles, Design, Selection, Construction, and Debugging of Air Source Heat Pumps!

A heat pump is a device that transfers the thermal energy from a low-temperature heat source to a high-temperature heat source. The low-temperature heat source commonly used in heat pump devices is the surrounding medium - air, river water, seawater, urban sewage, surface water, groundwater, reclaimed water, fire water tanks, or auxiliary working fluids discharged from industrial production equipment, which often have similar temperatures to the surrounding medium. According to different low-temperature heat sources, heat pumps can generally be divided into: air source, water source, and ground source.

Basic principle of air source heat pump water heater

It mainly consists of a compressor, heat exchanger, axial fan, insulated water tank, water pump, liquid storage tank, filter, throttling device, and electronic automatic controller. After the power is turned on, the axial flow fan starts to operate. The outdoor air undergoes heat exchange through the evaporator, and the cooled air is discharged from the system by the fan. At the same time, the working fluid inside the evaporator absorbs heat and vaporizes, and is sucked into the compressor. The compressor compresses this low-pressure working fluid gas into high-temperature and high-pressure gas and sends it to the condenser. The water that is forced to circulate by the water pump also passes through the condenser and is heated by the working fluid before being sent to the user for use. The working fluid is cooled into a liquid, which flows into the evaporator again after being throttled and cooled by the expansion valve. This cycle works repeatedly, and the heat in the air is continuously pumped into the water, causing the water temperature in the insulated water tank to gradually rise, finally reaching around 55 ℃, which is just suitable for people to take a bath.

A heat pump water heater consists of a compressor, condenser, evaporator, axial fan, liquid storage tank, filter, shut-off device, and electronic automatic controller. The compressor, condenser, evaporator, and throttling device are referred to as the four major components.

compressor

Function: A passive fluid machinery that elevates low-pressure gas to high-pressure. It is the heart of the refrigeration system, which sucks in low-temperature and low-pressure refrigerant gas from the suction pipe, drives the piston to compress it through the operation of the motor, and discharges high-temperature and high-pressure refrigerant gas to the exhaust pipe, providing power for the refrigeration cycle, thus achieving a compression condensation expansion evaporation (heat absorption) refrigeration cycle.

Common types: rotary type; Vortex type; Screw type household units generally use rotary type. Commercial units generally use vortex and screw types.

Rotary compressor

Working principle: The motor of a rotary compressor does not need to convert the rotational motion of the rotor into the reciprocating motion of the piston, but directly drives the rotating piston to perform rotational motion to complete the compression of refrigerant vapor.

Advantages: Due to the rotating motion of the piston, the compression work is smooth, stable, and balanced. In addition, rotary air compressors have no clearance volume and no interference from expanding gases, so they have the advantages of high compression efficiency, few components, small size, light weight, good balance performance, low noise, complete protective measures, and low power consumption. The conventional 1-2.5P uses a rotary compressor.

scroll compressor

Working principle: A scroll compressor is a compressor with a compressible volume composed of a fixed involute scroll and an involute moving scroll with eccentric rotational translation.

Advantages: The unique design of the scroll compressor makes it an energy-saving compressor in today's world. The main operating component of the scroll compressor, the scroll disc, only has a tight fit without wear, resulting in a longer lifespan and is known as a maintenance free compressor. The vortex compressor operates smoothly, with minimal vibration and a peaceful working environment, and is also known as the 'ultra static compressor'. The vortex compressor has a novel and precise structure, with advantages such as small volume, low noise, light weight, low vibration, low energy consumption, long service life, continuous and stable gas transmission, reliable operation, and clean gas source. Spiral compressors are generally used in small heat pump equipment, and the conventional 3-10HP uses a spiral compressor.

throttling device

Function:

1. Throttling and pressure reduction: The medium temperature and high-pressure liquid refrigerant from the condenser is throttled to reduce its temperature and pressure, making the refrigerant entering the evaporator a wet vapor with a lower saturation temperature, ensuring that the refrigerant boils at low temperatures to lower the temperature of the air entering the car.

2. Adjust the flow rate to automatically adjust the refrigerant flow rate based on changes in cooling load and engine speed, so that the refrigeration system always maintains the most suitable cooling capacity.

3. Prevent jamming and overheating. Control the refrigerant flow rate based on the temperature at the outlet of the evaporator to ensure complete vaporization of the refrigerant in the evaporator and prevent liquid hammer in the compressor; At the same time, control the refrigerant vapor superheat temperature to prevent the occurrence of abnormal overheating phenomena.

Common types: electronic expansion valve; Thermal expansion valve; Capillary tube.

thermostatic expansion valve

Working principle: The thermal expansion valve controls the flow of refrigerant entering the evaporator by sensing the degree of superheat of the gaseous refrigerant at the outlet of the evaporator. The thermal expansion valve consists of an induction mechanism, an actuator, an adjustment mechanism, and a valve body. The induction mechanism is filled with Freon working fluid, and the temperature sensing bulb is set at the outlet of the evaporator. There is a temperature difference between the outlet temperature and the evaporation temperature, which is usually referred to as superheat.

electronic expansion valve

Working principle: The controller calculates the parameters collected by the sensors and sends adjustment instructions to the drive board, which outputs electrical signals to the electronic expansion valve to drive its action. The electronic expansion valve takes only a few seconds to fully open from fully closed, with fast reaction and action speed, no static overheating phenomenon, and the opening and closing characteristics and speed can be manually set.

Characteristics: For thermal expansion valves, when the ambient temperature is low, the pressure change of the temperature sensing medium inside the temperature sensing chamber is greatly reduced, which seriously affects the regulating performance. For electronic expansion valves, their temperature sensing components are thermocouples or thermistors, which can accurately reflect changes in superheat at low temperatures. Therefore, in low-temperature environments such as freezing rooms in refrigerated warehouses, electronic expansion valves can also provide good flow regulation.

evaporator

Working principle: The evaporator is an important component among the four major refrigeration parts. The low-temperature condensed "liquid" passes through the evaporator and exchanges heat with the outside air, "vaporizing" and absorbing heat, achieving the cooling effect. The air source unit adopts a finned evaporator. The water source unit adopts plate heat exchangers.

condenser

Working principle: A device that quickly removes heat from a tube and converts gas or vapor into liquid. Common types: Shell and tube heat exchanger (conventional hot water unit), titanium tube heat exchanger (swimming pool unit), and sleeve heat exchanger (air-cooled module unit).

four-way valve

Function: The four-way valve is the main component used for defrosting in heat pump systems. A four-way valve consists of three parts: a pilot valve, a main valve, and an electromagnetic coil.

Working principle: A four-way valve is different from a regular direct acting solenoid valve. It must work under a certain pressure to function properly. A four-way valve consists of three parts: a pilot valve, a main valve, and an electromagnetic coil. The electromagnetic coil can be disassembled, and the pilot valve is welded to the main valve as a whole. When the solenoid valve coil is in a power-off state, as shown in Figure 1, the pilot slide valve moves left under the drive of the compression spring on the right side. High pressure gas enters the capillary tube ① and then enters the right end piston chamber. On the other hand, the gas in the left end piston chamber is discharged. Due to the pressure difference between the two ends of the piston, the piston and the main slide valve move left, causing the exhaust pipe (S pipe) to communicate with the outdoor unit connecting pipe (C pipe), and the other two connecting pipes to communicate, forming a heating cycle. When the solenoid valve coil is in the energized state, as shown in Figure 2, the pilot slide valve overcomes the tension of the compression spring and moves to the right under the magnetic force generated by the solenoid coil. High pressure gas enters the capillary tube ① and then enters the left end piston chamber. On the other hand, the gas in the right end piston chamber is discharged. Due to the pressure difference between the two ends of the piston, the piston and the main slide valve move to the right, causing the exhaust pipe (S pipe) to communicate with the indoor unit connecting pipe (E pipe), and the other two connecting pipes to communicate, forming a defrosting cycle.

Other components: sensors, pressure switches, refrigerant.

Selection of installation site for outdoor units:

1. Provide sufficient installation and maintenance space

2. The air inlet and outlet should be unobstructed and strong winds should not blow everywhere

3. Dry and ventilated area

4. The supporting surface is flat and can withstand the weight of the outdoor unit. It can be installed horizontally without increasing noise and vibration

5. Running noise and exhaust air do not affect neighbors

6. No flammable gas leakage location

7. Easy to install water inlet and outlet pipes and electrical connections

8. Recommended locations: balconies, outdoor air conditioning panels, rooftops, etc.

Attention: Installation in the following places may cause machine failure (if unavoidable, please consult): 1. Places with mineral oils such as engine oil; 2. Factories with severe fluctuations in power supply voltage; 3. Cars or cabins; 4. Kitchens and other places filled with oil, gas, and oil droplets; 5. Places with flammable gases or materials; 6. Places where acidic or alkaline gases evaporate; 7. Other special environmental conditions.

Selection of installation location for household water tanks:

1. Provide sufficient installation and maintenance space

2. The supporting surface is flat, able to withstand the weight of the outdoor unit, and can fix the water tank in the vertical direction

3. Non corrosive gas leakage location

4. Easy to install and connect water pipes and electrical connections

5. It is convenient for the water discharged during the operation of the safety valve to be smoothly discharged into the sewer

6. Ensure that the water discharged during the operation of the safety valve does not splash onto wooden floors and furniture

7. If the water tank is higher than the hot water outlet, a positive and negative pressure safety valve must be installed on the hot water pipe

The height difference between the water tank and the unit shall not exceed 3.5m

Attention: 1. Determine the correct moving path

2. Try to transport the machine in its original condition as much as possible

3. Please install the accessories according to the instructions in the water tank manual

4. Please place the water tank upright for installation