Showers become even more economic
Published: 08 March, 2013
Well over half the energy that goes down the drain as hot water from showers can be recovered to preheat cold water using simple maintenance-free technology. Jon Cockburn takes up the story.
In recent years heat recovery has become a key way to save energy — with waste heat generated by anything from boilers and ventilation systems to compressors and refrigeration plant often being put to good use. However, very useful heat can also be collected through shower heat-recovery units, which transfer heat from discharged waste water to the incoming cold mains water supply.
With the commercial sector being tasked with reducing its energy consumption and carbon emissions, and facing increasingly high energy costs, in recent years there has been a definite rise in the number of businesses utilising heat recovery.
Heat recovery systems essentially collect and reuse the waste heat generated by HVAC systems or heat-generating processing plant — whereas ordinarily this would be lost, and hence wasted.
Heat can be recovered from all sorts of appliances, machinery and equipment, such as boilers, ventilation systems, cooling systems, compressors, ovens, furnaces, kilns and dryers. Therefore, many types of commercial environments will have equipment installed on site from which waste heat can be recovered. An office, for example, could recover heat from its heating system, while a factory could reuse the heat generated by its compressors.
The recovered heat can be used within the actual process from where it was obtained, or for other purposes. Some common uses include pre-heating boilers, ovens and furnaces, pre-heating fresh air for ventilation systems, hot-water generation, space heating and drying.
And the savings can really stack up. In most cases, heat recovery is more efficient when the heat source is physically close to where the recovered heat is going to be used, and it’s preferable for it to occur at the same time. Generally, the higher the temperature, the greater the value for heat recovery. Compressors, for example, generate a lot of heat — of which around 85% can actually be recovered.
Recovering heat from equipment such as boilers and compressors has definitely become more commonplace in recent years, but perhaps a less well-known solution is the shower heat-recovery unit (SHRU), where useful heat is recovered from discharged waste water.
Shower heat recovery has primarily been developed for the domestic market in response to the UK Building Regulations. In new-build domestic properties, SHRUs are helping developers, architects, specifiers, contractors and installers to meet their SAP requirements cost effectively. As well as reducing a property’s carbon footprint, SHRUs also offer end users reduced fuel bills and increased comfort.
Although shower heat recovery products are largely installed in new-build developments, they can also be fitted in existing properties, and are included in the Green Deal. When fitted retrospectively, running costs can deliver savings which are comparable with solar thermal.
Furthermore, SHRUs can also prove to be a cost-effective, energy-saving solution for offices, factories and processing plants with onsite staff showering facilities.
SHRUs comprise a length of pipe within a pipe (known as a pipe-in-pipe design), which forms part of the vertical section of the waste drain pipe leading to the soil pipe. As an example, our product — the Itho SHRU 60 — is a straight, 2 m length of copper pipe with another copper pipe inside, with a 42 mm total diameter.
The concept is actually very simple; the waste water from the shower is discharged through the inner pipe, while the clean, cold water flows through the outer pipe. Hence the heat from the discharged waste water — which otherwise would be lost — is transferred to the incoming supply feeding the shower.
When hot water from a shower goes down the drain, it loses only a couple of degrees, so it’s a very useful heat source. In fact, the outgoing water is capable of heating the incoming water by around 15 to 19°C. Therefore, as the energy required to heat the shower water to the desired temperature is reduced, taking a shower can cost less — or can last longer using the same amount of hot water as before.
As its name suggests, the SHRU 60 recovers approximately 60% of energy. Independent tests to NEN 5128 A1:2009 standards have been carried out using a shower with a flow rate of 7.5 l/m with mains water coming in at 10°C and a desired hot water temperature of 40°C. They have demonstrated that the SHRU 60 can raise the incoming water to 28.2°C — with 9.45 kW of energy being recovered (which would normally have been required to heat the shower without an SHRU 60).
As well as offering energy saving benefits, SHRUs are hassle-free. They don’t require any regular maintenance or end user interface, and there are no moving parts or components to potentially fail.
With carbon-reduction commitments to meet and escalating energy costs to consider, organisations should be considering new ways to obtain free energy. Though SHRUs are primarily being seen as a way to meet SAP requirements on new-build developments, businesses with a small number of onsite showers could reap benefits too.
John Cockburn is head of marketing at Heatrae Sadia.