[Paper Review] Feasibility study and thermoeconomic analysis of cooling and heating systems using soil for a residential and greenhouse building

Morteza Bodaghi, Kazem Esmailpour+1 more|arXiv (Cornell University)|Apr 11, 2023

Greenhouse Technology and Climate Control6 citations

TL;DR

This study proposes a soil-based ventilation system for residential and greenhouse buildings, using buried pipes to transfer heat via air flow for passive heating and cooling. Results show it reduces summer peak temperatures by up to 15°C and increases winter minimums by up to 7°C, with the air-based system proving more effective and less costly than conventional HVAC, especially in hot climates like Abadan and Rasht.

ABSTRACT

In the past decade, the use of renewable energy for heating and residential and greenhouse cooling structures has gained much interest due to the energy crisis, population growth, and the quantity of demand. This paper investigates heat transport and thermodynamic equations for a residential and greenhouse structure to simulate and examine the performance of a soil air conditioning system using fluid flow rate, pipe diameter, length, and fluid type features. The results show that the air-driven ventilation systems during summer outperform the rest of the HVAC systems. Moreover, decreasing the diameter and prolonging the pipeline positively affects the ventilation system's performance. In addition, the airflow rate positively correlates with our HVAC performance. We studied the performance of the air-conditioning systems in 4 cities in Iran. The Rasht's ventilation system is claimed to be the most effective for heating, and the Abadan cooling system showed outstanding results. We also compared the expenses of the soil cooling and conventional HVAC systems.

Motivation & Objective

• To evaluate the feasibility of using soil as a thermal reservoir for passive heating and cooling in residential and greenhouse buildings.
• To analyze the thermodynamic performance of soil-based ventilation systems under varying pipe dimensions, fluid flow rates, and climate conditions.
• To conduct a thermoeconomic comparison between soil-based ventilation systems and conventional split-system HVACs in terms of capital and operational costs.
• To identify optimal system parameters (pipe diameter, length, flow rate) that maximize thermal performance and cost efficiency.
• To assess regional performance differences across four Iranian cities with varying climates—Tehran, Tabriz, Abadan, and Rasht.

Proposed method

• Developed energy balance equations for building components (walls, floor, greenhouse) to model heat transfer between indoor air, building surfaces, and the environment.
• Simulated heat transfer through buried pipes using fluid flow rate, pipe diameter, length, and fluid type as key variables, with soil temperature as the thermal sink/source.
• Applied thermodynamic principles to model heat exchange between air flowing through pipes and the surrounding soil, using convection and conduction equations.
• Used computational modeling to evaluate system performance across different cities, varying pipe geometry and airflow rates.
• Conducted thermoeconomic analysis by comparing initial investment and electricity costs of soil-based systems against conventional split-system HVACs.
• Incorporated real-world pricing data for pipes, blowers, and electrical consumption to estimate total system costs.

Experimental results

Research questions

• RQ1 How effective is a soil-based air ventilation system in reducing peak summer temperatures and increasing winter minimum temperatures in residential and greenhouse buildings?
• RQ2 How do pipe diameter, length, and airflow rate affect the thermal performance of soil-based HVAC systems?
• RQ3 What is the thermoeconomic advantage of soil-based ventilation systems compared to conventional split-system HVACs in different Iranian climates?
• RQ4 Which city-specific climate conditions yield the highest performance and cost efficiency for soil-based heating and cooling?
• RQ5 Is air-based soil ventilation more effective and economical than water-based alternatives in the same system configuration?

Key findings

• In Abadan, the soil ventilation system reduced summer maximum temperatures by 15°C and increased winter minimums by 4°C in the greenhouse, outperforming other cities.
• In Rasht, the system achieved a 13°C reduction in summer peak temperatures and a 5°C increase in winter minimums in the greenhouse, indicating strong performance in moderate-humid climates.
• The air-based soil ventilation system reduced summer peak temperatures by up to 14°C in Tehran and 11°C in Rasht, with winter heating gains of 4–7°C depending on location.
• Increasing airflow rate improved summer cooling performance, with a 24-hour operation costing only $2.85 for the air blower, significantly lower than the $24.08 for a split system.
• The total system cost for soil-based ventilation ranged from $250 to $350, which is substantially lower than the $9,000–$12,000 cost of a conventional split system with copper piping and insulation.
• Soil-based air ventilation outperformed water-based systems in thermal performance, with lower energy use and higher temperature regulation efficiency, especially in summer.