Rain Harvesting

What is Rain Harvesting?

Rainwater harvesting systems collect rainwater from the roof of a building, then filter it before storing it for use in non-potable applications such as toilets, outside taps, and washing machines. The rainwater is stored in large tanks that are usually buried underground but above ground tanks can be used if required.

How Does it Work?

There are different types of rainwater harvesting systems, but the principle on which they operate is similar. All Green Energy Doctor whole house systems consist of two main components:

Storage Tank
The air is extracted from specific rooms (specifically, kitchens, bathrooms and cloakrooms) using an efficient fan that is housed in the centrally mounted unit. As the air passes through the unit, the heat is transferred to incoming outside fresh air that has been filtered to prevent the ingress of airborne pollutants such as pollen and dust. The system works by enabling the two air streams (in and out) to move close to one another without actually mixing. In this way, one air stream warms the other. This is done inside a counter- flow heat exchanger, which is made up of hundreds of individual air channels.

Pump and Control System
The main unit is connected to each room via a number of flexible or rigid ducting tubes that allow air to be drawn from and delivered to the specific rooms. These ducts can be hidden within internal walls and ceilings of the property. This is a very simple process for new build or existing properties of one floor, but may take a little more work for existing properties with more than one level.

Is It Suitable For My Requirements?

Which system is most suitable for your property or project depends on a number of factors that Green Energy Doctor will take into account as part of the design. However, the following are some general principles that will help you decide whether it is a technology you would like to consider in more detail for your property or project:

Positioning & Location
In our experience, only a small percentage of sites are suitable for wind turbines to gain the benefit required to make them economical. It is critical in siting a wind turbine that it is well clear of large obstacles, especially in the path of the prevailing wind. There has to be a good line of sight from the turbine. If the turbine is too near to large obstacles such as buildings, trees or hills the true potential of the system will be difficult to attain. As a general rule:

• If the turbine has to be placed behind an obstruction, it should be ten times the height of said obstruction.
• If the mast is to be placed in front of a building, to avoid any turbulence, it should be twice the height.
• They are of limited effectiveness in built up urban areas

Water Requirements
One disadvantage is that wind power is an intermittent power source. The production from a wind turbine may increase or decrease dramatically over a short period of time with little or no warning. Therefore, turbines are used, generally, to supplement other sources of power as from solar panels or the National Grid.

What Are The Benefits?

Reduce Your Water Bills
For those who do ventilate their property sufficiently, it is estimated that on average, 20% of the energy delivered to buildings is lost through departing ventilation air streams. In more modern buildings, the proportion of airborne energy loss can be even greater: up to 30%, due to the higher standards of thermal insulation. Extract ventilation systems can account for a significant proportion of overall building heat loss. Installing a heat recovery ventilation system could help reduce your energy costs.

Energy Efficiency
Although the system uses a fan to drive the air, it is an extremely efficient motor that means the system still deliver energy positive ventilation compared to non-heat recovery methods. The heat exchanger is effectively collecting heat from the air leaving the building and reusing the energy to heat the incoming fresh air. This means that the energy that would otherwise be lost is used to heat the incoming air, helping to maintain a comfortable temperature.

Comfort
The system also eliminates the need for noisy bathroom extractor fans, window trickle vents or open windows. Therefore you can relax in a clean draught-free environment.

Security
By not having to open any windows, but still have a fresh environment you can constantly lock your windows meaning that your security will be improved.

This technology is only recommended if you are completely refurbishing your home, or if you are building a new home, as pipes needs to be run from the tank under the garden to the toilets and washing machine. The typical pay back time for a family home on metered water is about seven years.

How Much Does It Cost?

The cost of a Green Energy Doctor rainwater harvesting system will depend on the tank size and the complexity of the installation. Typically, a system for a family home costs less than £2,000.

Once a technical survey has been carried out, all Green Energy Doctor prices will be given as fixed prices.