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Supply and demand options of hot water

The industry’s suppliers discuss the dual aspects of water heating and refurbishment in H&V News’ latest special report.

An essential part of any HVAC installation, the provision of an effective hot water system is an important consideration. The various options available can add considerably to the savings and efficiencies delivered and can equally detract if mistakes are made.

Dimplex marketing communications manager Karen Trewick says the cost of water heating now accounts for a much higher proportion of consumers’ energy bills as space heating has become more efficient. With the UK entering a new ‘age of austerity’ and consumers wanting to economise, energy-efficient water heating can offer a way to reduce running costs, she says.

Key trends

People use 55 per cent more water now than in 1980 and each of us now gets though around 45 litres of hot water every day. A water heating system that only heats what’s used can go a long way towards keeping a rein on costs.

In addition, we now live in less space than our parents did. A survey by the Commission for Architecture and the Built Environment says the average new home in the UK has 76 sq m of floor space, compared with 113 sq m in France and a staggering 214 sq m in the US. This demand for small properties is fuelled by increasing house prices and more single-person households. In short, space in UK homes is at a real premium.

Electric unvented water heating cylinders can offer efficiency, economy and space saving, Ms Trewick continues. They provide mains pressure hot water supply for fast filling baths and powerful showers and eliminate the need for a cold water storage tank, making them ideal to free up valuable living space.

Alternatively, solar thermal water heating can offer even greater energy efficiency. Able to provide up to 60 per cent of a property’s total water heating needs, it offers a fast, lower-cost option compared with some renewable solutions. Installing as a retrofit is both relatively easy to do and cost effective for the user, and is also covered by the Renewable Heat Incentive (RHI).

With electric unvented cylinders ideal for meeting the water heating requirements of today’s homes and demand for solar thermal set to grow, forward-thinking installers will be looking to utilise these systems at every opportunity, says Ms Trewick.

Loss prevention

Zip UK marketing director David Bradbrook says any centralised hot water system can use instantaneous water heaters to bring real efficiency benefits, avoiding energy loss associated with long pipe runs when central systems serve remote locations. Further wastage can occur when water is drawn off before hot water is available.

Instantaneous electric point-of-use water heating systems have become more sophisticated in operation, he says, and some now feature electronic power control for enhanced temperature stability, incorporating elements positioned directly in the water flow path to ensure fast heat up.

These units are typically located below and a short distance from standard taps, keeping losses to an absolute minimum, Mr Bradbrook claims.

They can also offer significant savings over point-of-use storage water heaters, as these will have some level of standing heat loss.

The familiar surface-mounted electric hand wash unit has rarely been considered a stylish solution and their over basin location has often made them susceptible to vandalism.

The latest generation of in-line instantaneous hot water heaters successfully tackles these challenges, says Mr Bradbrook. They eliminate water wastage, standing heat losses and distribution losses, including those resulting from hot water standing in pipes. They are also more stylish and compact, installed out of sight below hand-wash basins, and can be connected to conventional or touch-free taps, he suggests.

Growing awareness

ICS Heat Pump Technology managing director Garry Broadbent (pictured) says the market is becoming aware of the heat pump opportunity and there is considerable potential for domestic and sanitary hot water production through suitable dedicated applications.

A heat pump connected on a standard Y or S plan basis allows it to prioritise DHW production and a high temperature model will provide a high-stored DHW temperature 365 days per year, due to its ability to provide a 65 deg C output.

This differentiates the high temperature heat pump from the medium temperature output units which will not be able to deliver this higher temperature, he says.

However, a new range of twin simultaneous heating and DHW output machines are now also available. There is nothing new about a de-superheater (heat exchanger) being fitted to a heat pump or chiller to provide a percentage of high temperature output energy; however, this new range goes further.

The primary (de-superheater) heat exchanger is sized at 100 per cent of the heat pump duty rather than a more conventional 25 per cent, which means that the heat pump is able to provide full capacity on either heating or DHW output.

It is fitted with a modulating pump which allows the heat pump to ‘pulse’ the hot water cylinder with an output temperature generally around 20 deg C higher than the heating output.

Medium temperatures with immersion back up will be acceptable for smaller applications but a higher temperature option would be attractive for larger applications, says Mr Broadbent.

The refurb route

Envirotec AHU refurbishment manager Ron Flewett highlights the benefits of refurbishing installations as organisations look to reduce their energy consumption.

Not only does this reduce the raw material consumption and its embedded carbon footprint, it can also effectively upgrade existing plant to the latest standards, he suggests.

A good example of this principle is air handling units (AHUs).Consider a 2x2x6 m AHU with an airflow of 7 cu m/s, he says.

Incorporating a volume control damper, a bare tube frost coil (LPHW), panel filters to F4 efficiency, bag filters to G6, a CHW cooling coil, a LPHW reheat coil, a fan and electrically powered motors.

To supply and deliver a new AHU would cost approximately £12,500, says Mr Flewett. To refurbish a similar unit by replacing all internal components, treating corrosion, replacing damaged external panels, re-commissioning and providing a 12-month warranty would cost around £9,500.

When you include additional costs such as fitting of new ductwork and refitting the connections, the savings, compared with buying new, can increase up to 50 per cent, he claims. Also, when longer lead-in times and the potential disruption of delivery and onsite fitting are taken into account, AHU refurbishment starts to look even more appealing.

The first stage is an initial inspection to assess the current condition, the potential for refurbishment and the cost implications.

Remaining with the AHU example, clearly all components will suffer some age deterioration, but this will have affected some more than others, says Mr Flewett.

Cooling coils, for example, may have suffered a corrosive oxidation effect. There will also be considerable wear and tear on moving parts in fans and motors, while static components may have years of life left in them.

In addition, refurbishment options should include mechanisms for reducing energy consumption, perhaps by using newer, more efficient designs of component that comply with modern standards and specifications.

The efficiency of fans, fan motors, heating and cooling coils, insulation and direct expansion equipment can all be improved in this way. With larger items of equipment there are also access considerations.

Once the evaluation has been completed, a method statement and risk assessment can be produced, along with detailed costings to facilitate the decision making process.

Clearly, these same principles can also be applied to other plant. The key is the application of specialist expertise to assess the situation and arrive at the best solution, Mr Flewett concludes.