Design strategies for zero carbon hot water
The leisure industry is a diverse sector encompassing a broad range of facilities from outdoor sport spaces to large fitness complexes. While the nature and size of the venues will vary, a common requirement is the assured availability of efficient, reliable and safe hot water, including during peak demand. As organisations look to reduce the carbon intensity of heat in their facilities, Andy Green, Head of Technical Solutions at Baxi, explores all-electric hot water design options for shower facilities in caravan and camping parks and sports pavilions.
As local authority officers and leisure facility operators work towards meeting their wider sustainability and climate targets, hot water as well as heating services will be a natural focus in all buildings. All-electric solutions, typically involving heat pumps combined with storage and renewable energy technologies, offer opportunities to move to Net Zero operation domestic hot water (DHW) systems. But an understanding of the usage and occupancy profiles of the facilities will be key to engineering the most efficient and cost-effective solution.
To explore this in more detail, let’s consider different approaches to DHW delivery, based on demand type, for shower facilities in caravan and camping sites compared with those in park sports pavilions.
Caravan and camping sites
At caravan and camping sites, the occupation profile is mainly seasonal, typically running from March to October. In terms of DHW usage patterns, the total volume of hot water used is high, but the demand may be spread over several hours or follow a morning and evening peak pattern.
One all-electric design option for this hot water usage profile might be to combine an air source heat pump (ASHP) with a large unvented cylinder. Factoring in the relationship between storage and recovery times is critical for maximum performance and efficiency. The design should therefore ensure that the ASHP is prioritised to pre-heat the water in the cylinders and that the heat is recovered in time to meet the next demand. As a fail-safe for periods with an unusually high draw of hot water, a back-up immersion heater can be used to maintain the water temperature and to ensure that the cylinder is pasteurised where necessary.
Advantages of this DHW system design are the high efficiency it delivers and low standing losses. While we wait for the government to address the ‘spark gap’, or price ratio between gas and electricity, operators should consider making use of nighttime low off-peak electricity tariffs for more cost-effective operation. Integrating solar PV panels or solar thermal technology should also be a consideration as a means of increasing energy resilience and addressing the current cost imbalance.
A case in point is the new state-of-the-art shower facility at Pembrey Country Park, run by Carmarthenshire County Council. M&E consultant Pursey and Ball specified a Baxi Auriga HP 40 ASHP combined with a 1,000l Megaflo Flexistore unvented cylinder and immersion heater to satisfy the project requirements. The highly efficient system reliably provides sanitary hot water provision for the hundred plus campers visiting the park. Water saving fixtures and 10kW of solar PV panels contribute to the Net Zero operation, providing a practical, sustainable solution that meets the council’s objectives and Welsh Building Regulations for new-build developments.
Sports pavilions
Sports pavilion shower facilities have a much more sporadic occupancy profile than those in camping and caravan sites. The pavilion showers may be left unused for most of the week and then be hit by intense high demand due to weekend football, rugby or cricket matches. Where matches are held concurrently as well as back-to-back, there can be as many as 50 people requiring hot showers simultaneously with only a short recovery period before the next match ends.
The challenge is to design a system that will meet the short but intense high DHW usage in the most efficient way. Clearly, storing vast volumes of water that will only be used twice a week makes no sense. An instantaneous solution, often involving direct electric cylinders and/or point of use water heaters, will ensure zero standby heat loss and rapid recovery. But it may require higher electrical demand than can be supported by the small pavilion. In such cases, thermal storage batteries often provide the best answer.
An interesting example is the Grade 2-listed Eaton Park Pavilion. When refurbishing the building, the decision was made by Norwich City Council to replace the existing gas system with an all-electric heating and hot water solution based around ASHPs. Designed by J D Gray & Associates, the new system involves two roof-mounted low-profile Baxi 13kW ASHP units, two buffer vessels and two Baxi 300l ASHP cylinders. The design also includes 66 solar panels which charge two 8kW batteries. The excess energy from the batteries powers the immersion heaters in the hot water cylinders to ensure rapid recovery and meet the intense DHW demand. Extension timers mean that the system can be brought on quickly to meet any out-of-hours or out-of-programme use requirements. By prioritising solar energy, the solution reduces reliance on grid electricity and lowers bills by converting surplus energy into heat, meeting the council’s sustainability objectives.
Manufacturer support
In both these examples and indeed on all projects, a deep understanding of the usage and occupancy profiles and lifecycle maintenance requirements (a whole article in itself!) is critical to meeting project requirements with the most efficient DHW systems. Of course, there is no silver bullet solution. A hybrid combination of ASHPs and gas-fired water heaters may be a more pragmatic approach for sites where gas is to be retained, for example. Use of solar energy and off-peak energy tariffs should also be considered when engineering the solution to drive down electricity costs and improve resilience.
For this reason, it is beneficial to partner with a manufacturer who can provide full wraparound services from initial site visits to commissioning and ongoing maintenance. As an experienced heating and hot water solutions provider, we at Baxi look forward to supporting consultants, contractors and leisure facilities managers with our technical design expertise, wide portfolio of low carbon solutions and service packages to achieve and maintain the best solution every time.
