Seven questions to ask your geoexchange installer
Designing and installing a geoexchange system involves more than just shoving a few pipes in the ground and hoping for the best. Here are seven key questions you need to ask your geoexchange installer to ensure you get the best possible system.
This topic has been inspired by feedback we receive from home owners, builders, architects and installers from around the country. We received it again recently after a home show event and it usually starts with something like:
“My (insert relationship to person telling story) installed one of those geothermal systems and it (insert outcome where the system didn’t perform up to expectations).”
Of course, this immediately piques our interest so we explore further. Inevitably, the story unfolds of how it was a DIY attempt by the home owner or, even worse, an effectively DIY attempt by a tradesperson who promised to ‘have a go’. Even worse, a tradesperson who is openly selling and installing systems that do not conform to international best practice or who is intentionally using substandard equipment to save some dollars on the install cost.
After all, how hard can it be? All you do is lay some pipes in the ground, pump water through them and connect them to a heat pump — and voila! A geoexchange system. The concept is indeed simple. However, like all great systems, the art of the science is in the subtleties and nuances that integrate the different elements of the system and ensure great results.
It is easy to sell a geoexchange system cheaply. You simply ‘short loop’ the ground heat exchanger and import/build your own substandard ground source heat pumps to reduce the install cost. The nature of the technology is such that it may well perform adequately for a few years. Great for the installer who has received payment and moved on, not so great for the home owner.
However, ‘adequate’ performance for a few years is not good enough with geoexchange systems. Fifteen years of highly efficient operation and subsequent energy savings should be the bare minimum. This is an industry benchmark that surpasses all other systems and it is the benchmark to which geoexchange systems should comply.
Here are seven key questions you should ask your geoexchange installer to ensure that you get the right system for your facility.
1. Are you IGSHPA certified?
Awkward acronym; sensible choice. IGSHPA, the International Ground Source Heat Pump Association, pioneered installation in the ground source heat pump industry and has more than 25 years’ experience in conducting installation and design workshops. IGSHPA collaborates with Association of Energy Engineers to teach the Certified GeoExchange Designer course.
By engaging an IGSHPA-accredited installer and/or designer, you can trust that accredited installers have been taught detailed failsafe information.
2. Does the proposed installation comply fully with the IGSHPA guidelines?
The IGSHPA guidelines exist not to create more red tape but to ensure that best practice is followed in the design and installation of a geoexchange system. What this means is that the system will be tailored to the needs of the application, taking into account heating and cooling requirements, soil type, ground temperature and scalability.
For instance, the IGSHPA guidelines outline specific installation details such as the types of join required for the pipes. While this level of detail may seem nitpicky, cheaper methods of installation may work initially but will degrade over time, reducing the system’s effectiveness and even resulting in outright system failure. The guidelines ensure that the system operates optimally.
3. Do you use industry-recognised heat load calculation software to calculate the heating and cooling requirements of the project?
Modelling is hugely important to the design of a geoexchange system. Using high-quality heat load calculation software helps the client understand just how much heating and cooling a facility requires, giving the designer the ability to tailor the system precisely to the facility’s specific needs.
While a system that’s too large for a facility will certainly meet its requirements, installing an oversized system can hit the client in their hip pocket.
Specifying a geoexchange system that’s 20% larger than required, for instance, means that 20% more boreholes need to be drilled to install that system — resulting in the client paying 20% more for labour and parts than they need to.
Similarly, an undersized system won’t be able to keep up with demand, meaning that the system won’t meet the heating and cooling needs of the facility.
If the design process doesn’t involve extensive modelling of heating and cooling requirements, you’re likely to end up with a system that won’t do the job — or one that will cost far more than it ought to.
4. Do you consider all types of ground heat exchanger for my system?
The two main components of a geoexchange system are:
- The ground source heat pump (GSHP) or geothermal heat pump, which provides the mechanical component of the system.
- The ground loop or ground heat exchanger (GHX), which provides the passive component of the system.
The GHX is the component that extracts the heat from the ground in winter or returns it to the ground in summer. They are classified as either open loops or closed loops depending on how they utilise the water flowing through the system. In some instances, they can be coupled to conventional chillers/boilers as a hybrid system.
Closed loops are constructed of polyethylene (PE) pipe and continuously circulate the same water for many decades. They can be either a vertical (borehole) or a horizontal (trench) configuration and some are even located in surface water bodies such as dams and harbours.
The loop fluid is simply circulated through the ground loop and returned to the ground source heat pump. In accordance with the zeroth law of thermodynamics, the loop fluid and the ground will endeavour to reach a thermal equilibrium.
Thus during its passage through the ground, the loop fluid is equilibrating with the stable ground temperatures either by extracting heat from the ground (winter) or rejecting heat to the ground (summer). The extent of this equilibration is determined by the residence time in the ground, the temperature differential between the loop fluid and the ground and other ground properties such as thermal conductivity and thermal diffusivity.
There are three types of closed loop system: horizontal GHX, vertical GHX and closed water loop heat exchanger.
- Horizontal closed loops (Figure 1) are installed when there is sufficient land area available and soil depth permits excavation to an approximate depth of 1.5 m. Multiple pipes can be laid in the trench and the total length of the trench is a function of the heating/cooling load.
- Vertical closed loops (Figure 2) are installed where land area or shallow rock does not permit the installation of a horizontal loop. Boreholes are drilled to depths of 50 to 120 m. The depth, number and spacing of the boreholes is a function of the heating/cooling load.
- The closed water loop heat exchanger (Figure 3) uses a dam, pond or lake. Polyethylene coils or stainless steel plate heat exchangers are installed in the water to provide a low-cost, highly efficient system. The water needs to be a minimum of 1.8 m deep at its lowest level during the year.
Figure 1: Horizontal closed loop system.
Open loops (Figure 4) utilise ground or surface water directly, pass it through a heat exchanger and then return the water to either its origin or a secondary application such as irrigation, industrial water etc.
An open loop system uses groundwater from an ordinary well or water bore. The groundwater is pumped into the heat pump unit where heat is extracted and the water is disposed of in an environmentally safe manner.
Because groundwater is a relatively constant temperature year-round, this is an excellent heat source.
5. Do you include soil type and ground temperature in the ground heat exchanger calculation?
This matters! Don’t believe any installer who tells you otherwise. What works in one location may well not work in another. Just as each facility is different, so too is each geoexchange installation. Soil type and ground temperature can significantly impact on a system’s efficacy, so they must be taken into account during the design phase.
6. Can you tell me the annual water temperature range in my ground heat exchanger?
As with all the previous points, your installer should be able to show that they have factored these aspects into the design. Calculating the annual water temperature range in a GHX is part of this. If your installer doesn’t do it, they’re not doing the job properly and you could be left with a geoexchange system that doesn’t do what you need it to.
7. Does your geoexchange software use climate ‘bin’ data to ensure that the system will work long-term and that it will not overheat or overcool the ground over a 20-year period?
Climate ‘bin’ data exists for every location with weather data. It shows how many days per year the temperature exceeded 42°C; how many days were 39–42°C; and so on. Inputting this data into the geoexchange software ensures that the system is capable of working at maximum capacity. It demonstrates that the system works at all extremes of operation.
If a geoexchange system isn’t designed correctly and there’s an imbalance between the amount of heat coming out of the ground and the amount going back in, this can cause big issues. If the system removes all warmth from the ground, it can freeze, eventually killing gardens and destroying building foundations. There’s far more at stake here than just heating and cooling!
You wouldn’t engage an unlicensed builder, plumber or electrician to build your facility. For the same reason, make sure you are speaking with an IGHSPA certified installer and that the system complies with IGHSPA industry guidelines.
The Geoexchange Accredited Installer Network (GAIN) provides you with peace of mind that you are speaking with a professional who works to international best practice. GAIN is the most experienced and qualified team of geoexchange professionals in the country.
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