Ground Source Heating

Why Ground Source Heating

Although we design all sorts of heating and cooling systems, we have become one of New Zealand’s main Ground Source Heating (GSHP) residential designers, these systems are different from Geothermal systems that extract the heat directly from active lava areas like Rotorua and Lake Taupo.

Although we can use GSHP’s to replace normal AC systems we generally use them for hydronic systems like underfloor heating and ducted fan coils.

An air source system extracts its low temperature heat from the air around the heat pump via a large fan blowing over the heat exchanger, the colder it gets outside the harder the system needs to work.

A GSHP differs by using the ground temperature as its heat source and at a depth of around 1.5mtr this is at a constant temperature so does not suffer from the large air temperature swings the air source units have.

There is a lot more to it than this, but it helps to understand why a GSHP is the most energy efficient way to heat a house in the world right now.

The Benefits to a Ground Source Heat Pump are;

• Running cost – Currently the cheapest way to heat a central heating system (unless you have free firewood and the time to chop it up each year).
• Noise – as there is no fan they run much quieter than Air source units.
• Location – again as they don’t need to be outside or require a flue they can be put anywhere in the house or garage etc.
• Maintenance – the only moving parts in a GSHP are two water pumps and a compressor both with long life spans.

Installing Collector Fields

As a GSHP uses the ground temperature we need to be able to extract this from the ground, there is many different ways to do this and each has its own cost and practicality, the main ways are as follows

1. Slinky trench – this is a trench 1.5mtr deep 1mtr wide and normally around 50mtrs long, in this trench we place a coiled up pipe stretched out like the slinky toys you used to send down the stairs as a kid, then the trench is back filled and covered for life. The number of trenches depends on the heat load of the house but a 200m2 house would most likely need 4 trenches if it was well insulated.
2. Bores – if you don’t have the ground area for trenches we can use drilled bores, this drills an 80mm diameter hole up to 100mtr deep with two pipes placed in it joined at the bottom, this is then back filled with a thermally conductive grout, a 200m2 house would need about 5 bores but each bore is quite expensive so a premium is payed for the easier collector field.
3. Ponds and Rivers – As we are just looking for a low temperature source we can put pipe in the bottom of a pond or river and extract energy from this, this is probably the cheapest way to create a collector filed but you do need either a large pond or flowing water on your property. Also, resource consent can be a bit of a process to get.
4. Open pits – If you already have a large area of land that needs building up to height we can lay pipes under this before you build the land up, all we need is the level raised over the pipes by 1.5mtr, this is overlooked a lot of times on commercial projects as an opportunity for a cheap collector field.

Knowledge Library

Rather than fill this website with the massive amount of information Kensa has on how ground source systems work and how they are installed please follow this link to their website 

 https://www.kensaheatpumps.com/knowledge-hub/