How to Build an Air Source Heat Pump: A Comprehensive DIY Guide

Building an air source heat pump (ASHP) can be a rewarding and cost-effective project for the DIY enthusiast. This comprehensive guide will walk you through the critical steps and technical specifications required to construct your own ASHP system, providing a detailed, expert-level playbook for a hands-on approach.

Calculate Heating Load

The first step in building an ASHP is to accurately determine your heating load. This will help you select the appropriate size of the heat pump unit for your space. You can use free online software or directly measure the energy consumption to calculate the heating load.

  • Heating Load Calculation: Utilize online tools like the Manual J calculation or the Department of Energy’s Heating and Cooling Load Calculator to determine the precise heating load for your home or building. These tools consider factors such as square footage, insulation levels, window sizes, and local climate data to provide an accurate estimate.
  • Direct Energy Measurement: Alternatively, you can measure the energy consumption of your current heating system to estimate the heating load. This method involves monitoring the energy usage over a period of time and extrapolating the data to determine the total heating requirements.
  • Sizing the Heat Pump: Once you have the heating load, you can select the appropriate size of the ASHP unit. As a general rule, in Oregon, you’ll need an 80-foot long, 3-foot wide, and 4-foot deep trench containing about 300 feet of slinky loops of plastic pipe per Ton (12,000 BTU/hr) of heating capacity.

Ground Source Loop Field

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The ground source loop field is a crucial component of an ASHP system, as it absorbs heat from the air and transfers it to the heat pump.

  • Trench Dimensions: The size of the trench for the ground source loop field will depend on the heating load and the local climate. In Oregon, for example, the recommended trench dimensions are 80 feet long, 3 feet wide, and 4 feet deep.
  • Slinky Loops: Within the trench, you’ll need to install approximately 300 feet of slinky loops of plastic pipe per Ton (12,000 BTU/hr) of heating capacity. This allows for efficient heat transfer from the air to the refrigerant circulating through the pipes.
  • Pipe Material: The most common material for the ground source loop field is high-density polyethylene (HDPE) or cross-linked polyethylene (PEX) pipes. These materials are durable, corrosion-resistant, and suitable for underground installation.
  • Pipe Insulation: Insulating the pipes in the ground source loop field is essential to minimize heat loss and improve the overall efficiency of the ASHP system. Use high-quality insulation materials designed for underground applications.

Heat Pump Construction

Building the heat pump itself can be a complex process, but you can start with repurposed components like air conditioners or dehumidifiers.

  • Repurposed Components: Look for used or discarded air conditioners or dehumidifiers that can be salvaged and repurposed as the basis for your DIY heat pump. These units often contain the necessary compressor, refrigerant, and other essential components.
  • Refrigerant Selection: When building a DIY heat pump, consider using Propane (R-290) as the refrigerant, as it is an environmentally friendly and efficient option. German children have successfully used Propane to cool their computer CPUs, which can inspire your ASHP project.
  • Compressor Compatibility: Ensure that the compressor you use is compatible with the refrigerant you’ve selected and can provide the necessary cooling and heating capacity for your heating load.
  • Coil Design: The design of the heat exchanger coils is crucial for the efficiency of the heat pump. Consult technical resources or seek guidance from experienced DIY heat pump builders to optimize the coil configuration.

Radiant Floor System

Integrating a radiant floor system can greatly enhance the efficiency and comfort of your ASHP setup.

  • PEX Tubing: PEX (cross-linked polyethylene) tubing is the most efficient material for a radiant floor system. It is durable, flexible, and easy to install, making it a popular choice for DIY projects.
  • Concrete Embedding: Embedding the PEX tubing in a concrete slab is a common approach for radiant floor systems. This process can be messy and requires careful planning and execution to ensure proper heat transfer and even distribution.
  • Insulation: Proper insulation beneath the concrete slab is essential to minimize heat loss and improve the overall efficiency of the radiant floor system.
  • Manifold and Zoning: Consider incorporating a manifold system and zoning capabilities to allow for individual room temperature control and optimize the heat distribution throughout your living space.

Installation and Integration

The final step in building an ASHP system is the installation and integration of the various components.

  • Ductwork Connections: Connect the return ductwork to the bottom of the heat pump unit and the supply ducts to the top. If your existing ductwork is not compatible, you may need to fabricate custom adapters.
  • Outdoor Unit Placement: Position the outdoor unit of the ASHP system near the indoor unit, ensuring easy access for maintenance and servicing. Secure the outdoor unit to a stable foundation.
  • Lineset Installation: Run a lineset, which is a pair of flexible copper tubes wrapped in insulation, to connect the indoor and outdoor units. Ensure proper insulation and sealing of the lineset to prevent heat loss and refrigerant leaks.
  • Electrical Wiring: Properly wire the ASHP system, including the indoor and outdoor units, as well as any necessary controls or thermostats. Consult local electrical codes and regulations to ensure safe and compliant installation.
  • Commissioning and Testing: Once the ASHP system is fully installed, commission the unit and perform thorough testing to ensure proper operation, efficiency, and safety.

Building an air source heat pump can be a complex but rewarding DIY project. By following this comprehensive guide and paying close attention to the technical details, you can create a highly efficient and cost-effective heating and cooling solution for your home or building. Remember to consult with local experts, follow safety protocols, and continuously monitor the performance of your ASHP system to ensure optimal long-term operation.