Sizing of systems
To specify the size of a system we use the results from extensive testing, and the experience gained through the review of previously installed systems, to apply understanding to various system designs.
Some general rules of thumb can be seen at the bottom of this section. Please be aware that these may 14 not be ideally suited to all scenarios, and so it is important to understand the demands and usage patterns of the building and its occupants before committing to specifying volumes and quantities of equipment.
Assistance to do this can be sought from our specification engineers and technical review staff who are available for consultation on such matters to the benefit of project planners of all types. It is advised that the details of any project enquiries be sent to our team, who will offer the best product specific solution available based on the information available at the time.
As with all projects, success often relies on the priorities of the intended design being clearly defined so these can be married with the operational characteristics of solar thermal technology, to achieve the best performance from the resulting integration of systems.
Factors that often influence the sizing of a system, which are often divisive to the performance targets of a text book system include; space limitations of plant areas, planning and building regulations targets which stipulate a percentage/quantity of energy to be achieved from renewable sources, and the peak demand and recovery target rates required of conventional fossil fuel fired systems which can remain un exercised compared with the sporadic solar yield characteristics which can reach and exceed their design capabilities on a regular basis in correlation with the weather conditions.
A typical LaZer2 system is capable of producing somewhere between 65-95% of the energy required for heating hot water in domestic buildings and achieve a payback period through energy savings alone of between 7-10 years. With a design life which well exceeds 25 years, this makes for a very viable addition to any building regardless of additional; moral, environmental and financial motives which may effect someone’s discussion.
Some customers who are more aware of the system characteristics and can be more flexible with their water usage patterns are able to avoid using any other heat source for the majority of the year. In buildings where the demand requirements are prioritised over the availability of free renewable energy, such as hospitals and commercial food preparation facilities, it is common that the supply of hot water on demand is ensured by conventional means whilst the solar is set up as a supplementary system to offset the maximum amount of fuel it can for the initial investment. The first item to tackle when sizing a system for domestic premises is what the stored hot water volume should be.
This will typically be 180ltrs < 250ltrs in most 2-4 bed homes in the UK. It would be recommended that any replacement cylinder be sized in accordance with this convention. For this size range of hot water system it would be recommended that 2 < 3 LaZer2 collectors be installed to heat the stored volume via an internal lower coil and the conventional heat source (boiler) be connected to provide supplementary/backup heating via a second internal upper coil.
This format is most appropriate for homes and assumes that the cylinder volume will be draw off and refilled for the most part on a daily basis. This approach can be scaled up for larger buildings such as university halls of residence, hotels or apartment blocks with centralised plant, as the typical volumes and usable patterns are comparable with self contained domestic properties. In offices and educational buildings, the use of hot water is likely to be slightly different and for the most part will be during normal working hours.
The volumes used for cleaning and in catering facilities will become the peak demands and had washing facilities will make up the remaining demands. The size of the solar system will revolve around the realistic daily quantity of hot water used by the building, and the number of collectors will be chosen in order that this volume is heated to the desired temperature on a daily basis for the majority of the year.
Because the design of the LaZer2 collector is such that the variation in performance throughout the year is due to the number of daylight hours and the clarity of light available, there are inevitably differences between the winter months and the rest of the year. The sizing of the system must take into account this and accept that in the winter months there may be a need to supplement solar heat with a conventional heat source, and in the summer the yield may exceed the demand on occasion.
It is important to get the balance right so as to provide as much of the hot water possible without losing efficiency through the system preventing the use of available solar energy because the stored hot water is too hot to apply further heating to it. 15 There is a balance between efficiency and effectiveness that needs to be evaluated and targeted when considering the number of panels and volume of water to be heated.
Effectiveness = the volume of water achieving or exceeding the desired minimum temperature in line with the demands of the occupants of the building.
Efficiency = putting to best effect, all the energy available from the sun in order to offset the maximum amount of energy otherwise obtained from conventional fuel sources, for the minimum of equipment cost.
Where the balance between the number of collectors (which equate to approx 1m= each) and the stored water volume falls below 65ltrs/m= there is a likelihood of an unusable surplus of solar energy, produced from the equipment during the summer months. This problem can be overcome if the design takes into account that the volume used each day is greater than 65ltrs/day resulting in a larger volume to be heated by solar each day.
On the other hand if the stored volume exceeds 85ltrs/day/m= of collector, then the system is less likely to achieve the required usable temperature other than in idyllic conditions during the summer months. In buildings where the temperature of a volume of water is required to be constant for the hot water system to work effectively, such as in some systems which incorporate heat stores or where legionella threats are considered very high. It is not very effective to incorporate solar thermal technology without having a rethink of the existing system design.
This is because the capacity for solar to add heat to water is not available if the water is already at the maximum safe temperature allowed by the system. The efficiency of the solar system is enhanced by a daily draw off and replacement of the cylinder volume with cooler water.
In hospitals and other types of public service buildings which have this scenario, the LaZer2 system can be configured to pre-heat water which enters the primary calorifier, allowing the primary calorifier and secondary return circuits to operate at higher temperatures between peak demand periods. Due to the slower recovery rate of solar compared with other heat sources, and the lower differential temperature between the primary and secondary sides of the solar heat input exchanger, stratification is often utilised to allow the hottest water to be available to the outlets whilst the coolest water to be introduced and remain near the heat input location for longer.
Many industrial or commercial hot water systems incorporate de-stratification in order to enhance the volume of water available for use and the reduce the potential for bacterial hazards. The LaZer2 system can be configured to achieve these priorities whilst also enabling the solar to work effectively providing some basic changes are made to the conventional hot water systems operation philosophy, and the volumetric demands of the property are attainable within the confines of the plant location.
When designing a system for heating a swimming pool it is again important to consider the intended result related to the achievable performance of different sizes of system. Here in the UK, for a typical below ground swimming pool of modern construction, average depth 1.5m, 30% of the pool surface area would be sufficient to provide a suitable level of heat input to reach desirable temperatures (26<30C)for what is considered to be the average British swimming season (May to September).
For pools with no other heat source, or pools with constructed such that greater than average temperature losses will be experienced, it is recommended that the percentage be increased to 50% or the surface area. Indoor pools which are well insulated (modern) it can be sufficient to reduce the area of solar collectors to as low as 15<25% of the surface area.
Often budget will affect the size of system chosen, but heating swimming pools can often be the most efficient use of solar thermal technology due to the relatively large losses and large volume of water they contain.