Geothermal Heating & Cooling in South Africa. Using the Earth to Heat & Cool our Buildings: A case for Ground Source Heat Pump Systems.
Sunny Southern Africa (and Africa) presently lags the international community when it comes to making use of Geothermal Energy to heat and cool our living and work spaces.
The earth is like a giant solar battery absorbing nearly half of the sun’s energy. A ground source heat pump system (GSHPs), also known as a geothermal exchange heat pump, is a heat pump that uses the Earth as either a heat source, when operating in heating mode, or a heat sink, when operating in cooling mode. The heat pump simply moves the heat from one area to another (it doesn’t make heat!). Your home refrigerator is a heat pump! These systems are a wonderful source of “green” renewable energy which is useful in any geographic location, particularly areas which have large seasonal air temperature variations. Over the past 32 years the geothermal industry has evolved and greatly expanded due to an increase of use and the aid of new technologies. GSHPs are widely used in USA, Canada, UK, Europe, China & SE Asia and Australia.
How Does a Ground Source Heat Pump Work?
The temperature of the ground a few meters beneath the Earth’s surface remains relatively constant throughout the year, even though the ambient air temperature fluctuates with seasonal changes. The ground temperature is surprisingly constant, and even at shallow depths of about 2 metres, the temperature of the ground in much of South Africa (and the world) remains pretty constant. The South African ground temperatures vary between 16.5o C and 21o C. This is the reason why groundwater pumped from boreholes, feels cool even on a hot summer day (27 – 35o C).
So in winter for example, heat is captured from the ground which is warmer than from the chilly air around your home. Conversely, in summer, the relatively cool ground absorbs a home’s waste heat more readily than the hot outdoor air.As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house or commercial building with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air. A GSHPs comprises of three basic elements – a ground loop, a heat pump, and an air / water distribution system (air ducting or water piping).
Efficiencies of Ground Source Heat Pump
The ground source heat pump is one of the most efficient residential heating and cooling systems available today, with operating efficiencies much higher than other heating systems and cooling systems. This means it directly translates into savings for you on your electricity bills. GSHPs generally have COP’s (Coefficient of Performance) of between 3 and 5! This means that for every unit of energy that you put in you get between 3 and 5 out! So it’s like having your own energy well but … it comes from your own premises, its free and renewable, environmentally friendly, available everywhere, heat’s cools and makes hot water! Buildings are responsible for between 30 – 60% of all CO2 emissions. By using this renewable form of energy you can directly reduce these emissions, particularly when compared to our fossil fired power stations. Installing GSHPs is environmentally responsible since it only transfers the heat, you or Escom need not burn any fossil fuels to create the warmth / cooling your home or office requires. GSHPs drastically reduce the CO2 emissions associated with other heating and cooling technologies. Good for you, good for the environment, good for Escom (no peak demands and less load shedding)! GSHPs lend themselves to zoned heating and cooling – one side of the building (facing the sun) could be cooled while the other side (facing away from the sun) could be warmed.
Free Hot Water
As a bi-product in summer GSHPs can designed to produce free hot water which can be used to either pre-heat your domestic geyser’s water or to heat the swimming pool! The heat comes from the waste heat extracted from the building when cooling. Types of Ground Source Heat Pump Systems
There are four basic types of ground loop systems. Three of these: horizontal, vertical, and pond/lake, are all closed-loop systems. The fourth type of system is the open loop option. Which one of these is best for your application depends on the nature of the building to be air conditioned, climate, soil/rock conditions, available land, and local installation costs at the site. All of these approaches can be used for residential and commercial building applications.
Closed Loop Systems
Horizontal
This type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. It requires trenches at least 2m deep. The most common layouts either use two pipes, one buried at 2m, and the other at 1.5m, or two pipes placed side-by-side at ~2m in the ground in a 0.5m wide trench. The Slinky™ method of looping pipe allows more pipe in a shorter trench, which cuts down on installation costs and makes horizontal installation possible in areas it would not be with conventional horizontal applications.
Vertical
Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, and they minimize the disturbance to existing landscaping. For a vertical system, boreholes are drilled about 10m apart and 100–150m deep. Vertical loop pipe is installed into these holes. The vertical loops are connected with horizontal pipes (i.e., manifold), placed in trenches, and connected to the heat pump in the building.Pond/Dam/RiverIf the site has an adequate water body, this may be the lowest cost option. A supply line pipe is run underground from the building to the water and coiled into circles at least 3m under the surface. The coils should only be placed in a water source that meets minimum volume, depth, and quality criteria.
Open-Loop System
This type of system uses groundwater or surface body water as the heat exchange fluid that circulates directly through the ground source heat pump system. Once it has circulated through the system, the water returns to the ground through the borehole, a recharge borehole, or surface discharge. This option is obviously practical only where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.
Open-Loop System – Standing Column
This type of system uses the vertical extent of a deep (120 – 250m) borehole which has high rest water levels (>20m). Groundwater is abstracted from the upper portions of the borehole used as the heat exchange fluid that circulates directly through the ground source heat pump system. Once it has circulated through the system, the water is returned to the deeper portions of the borehole. The water then exchanges heat with the borehole as it slowly moves up the column of water towards the pump.What do they look like?
Similar to refrigeratorsWhat are the Costs associated with GSHPs?
These systems have higher upfront costs than conventional Heating & Cooling systems due to the earth loop connections; however their payback time is between 5 and 10 years depending on the type of building (USA/Europe). Due to high efficiency and high heating/cooling capacity of GSHPs, they save the owner operational costs by requiring significantly reducing energy costs over the life span of the building. The ground loops are commonly guaranteed for +50 years and the heat pumps are extremely reliable, low maintenance units commonly running in excess of 15 – 25 years without any breakdowns.
Green Building Council – How GSHPs Benefit the Score
“On a practical level, a Green Building encompasses the use of design, materials and technology to reduce energy and resource consumption and create improved human and natural environments. Specific green building measures include careful building design to reduce heat loads, maximize natural light and promote the circulation of fresh air; the use of energy-efficient air-conditioning and lighting…” (Green Building Council of South Africa).
GSHPs provide up to 500% more efficient heating and cooling of buildings, use truly renewable energy, heat water as a by-product, cut’s significant Green House Emissions and allows for much greater building design flexibility as architects are not faced with the prospect of unattractive HVAC equipment on roof tops and can consequently employ a wider range of roof types (such as sloped roofs). Current trends dictate that more emphasis should be placed on climate change and energy resource depletion; GSHPs are one of the most potential green technologies available today.
GSHPs need investigation of the soil, rock and groundwater conditions beneath the site. GSHPs are far more efficient, cost effective in terms of lifecycle costs and environmentally friendly than conventional heating/cooling systems.
GSHPs are proven technologies the world over. 2010 – Ke Nako! It’s Time – that South Africa makes extensive use of such technologies.
For further information please contact Derek Whitfield of Environmental Drilling & Remediation Services on 082 456 8466 or derek@edrs.co.za
This document is a compilation of various sources of information, namely the International Ground Source Heat Pump Association (IGSPHA), Geothermal Heat Pump Consortium, National Ground Water Association.
