Opinion

Calculating costs

Bob Long, MD Eco Innovate Ltd
Bob Long, MD Eco Innovate Ltd

Heat pump trouble shooter Bob Long turns his attention to accurately quantifying system output and running costs

Renewable energy systems delivering their energy in the form of hot water are becoming increasingly more attractive as the cost of fossil fuels steadily rises.

Such systems generally represent significant financial investment, and the decision to install one or more of the available technologies should not be taken lightly.

Having made your choice, and installed a system, it is important that both the installer and the owner can quantify how much renewable energy the device is actually delivering.

Energy is generally measured in kW, and quantified in kW/hours.

For example, the size of an electric heater will be described in kW, and is easy to quantify, as each heating element or ‘bar’ generally represents 1kW.

By example, a very basic 3kW electric heater is likely to show three-bars visibly a bright orange colour, and is known to emit 3kW of energy.

This represents unquestionable value-for-money, as each electrical-resistance element consumes one kWh of electricity energy and, in return, delivers one kWh of thermal energy to its immediate surroundings.

Renewable energy devices are generally, less visual and therefore the output is not so easy to quantify.

Installers and owners need to know the answers to these questions:-

  1. 1.      How do I know that my investment in renewable energy is profitable?
  2. 2.      How do I know I made the right choice?
  3. 3.      How do I know if something goes wrong?

That fact is – you probably don’t!

Heat pumps are perhaps the most difficult of renewable energy devices to quantify, and made even more difficult with domestic electrical billing being quarterly, and retrospective.

A poorly performing heat pump system, or a system that has developed a fault, can cause excessively high electrical charges, and will often not be noticed until the bill arrives.

Quantifying actual running costs
Thermal energy can, of course, be accurately calculated, but with significantly more complexity than a simple electric radiator. To calculate the output of a renewable energy device, the parameters, listed below must be measured.

  • Flow rate of water in and out of the device in litres per second
  • Temperature differential of the water in and out of the renewable energy device
  • Specific heat of the water, or water/antifreeze mix

By measuring these values accurately, it is possible to calculate the amount of energy present in the water flow, and quantify the result in kWs.

Most users of renewable energy equipment will not have access to apparatus capable of measuring, and therefore will probably never know how effective their investment is.

Renewable energy system information module
Through advanced technology, we now have devices to collect, process, and calculate all of the above values, and display the result digitally in a LCD screen.

These devices will display the current real-time kWs of renewable energy being produced and a totalizer of the kWhs of energy produced within a determined period. All parameter values are available individually, which makes these units the most versatile and powerful diagnostic tool available. Clearly an essential system component.