Freezing Hot Water – Heat Recovery From Chillers to DHW

With commercial organisations being challenged to actively reduce energy demands and carbon emissions the application of heat recovery should be recognised as an important weapon in their sustainability arsenal. Typically applied to extracting heat from moist air in wet rooms or from showers for space heating applications, heat recovery in commercial scenarios can also be used to provision business-critical hot water.

Historically the deployment of heat recovery from large chiller/freezer units used as part of the day-to-day operations of restaurants and hotels, schools or universities with large-scale catering facilities & retailers holding frozen stock was one of the easier ways for a new build to attain required green credit. But with Net Zero now firmly on the agenda attention has shifted to a far more unilateral desire to reduce power demands and by association, emissions generated from buildings.

In 2015, Adveco began a process of development to create a Heat Recovery System able to utilise the waste heat from chiller (approx.1.5 kW) and freezer (2.5 kW) unit condensers to preheat the incoming mains water for commercial hot water installations. At this early stage of development temperatures as high as 45°C could be achieved with the heat recovery system and the primary heat source could be used to top up the water to 63°C. The waste heat would be used to heat a primary loop that would be piped to the water heater or preheat vessel to heat it indirectly through a coil heat exchanger.

For the initial development system, the heat recovery components including heat exchangers, pumps and controls built into the condensing units. However, the introduction to the market of new condensing refrigerant units, which are more efficient, allowed for heat recovery to be cut into the condenser high-pressure pipework. However, they did not provide the heat exchanger and controls. These units required a new approach, which led to Adveco developing the award-winning standalone HR001 Heat Recovery Unit.

The HR001 acts as an interface between chiller/freezer condenser units and the water heating system. Each HR001 box contains two separate chiller and freezer circuits that run through plate heat exchangers to recover heat into adjacent glycol refrigerant circuits, which are then pumped into the preheat coils of the hot water installation.

The box is supplied pre-packaged and ready to install near the condenser units. All components are pre-wired and installed within a grey IP rated housing with mounting brackets, allowing a quick and straightforward installation. The HR001 has its own isolator mounted on the side.

The HR001 connects directly to Adveco’s control panels for seamless integration into a water heating installation. The direction of flow for the heat reclaim is in the counter-flow direction to the refrigerant. Two AX differential temperature controllers each compare an S1 temperature to an S2 temperature and run their connected pump if S1 is at a higher temperature than S2. S1 is located in the refrigerant flow within the HR001. Both S2s are placed within the triple pocket of the tank in the water heating system (a feature unique to Adveco). The AX controls are both set to 60°C maximum S2 temperature, and 16°C differential between S1/S2. Indirectly pre-heating the incoming mains within a hot water installation, HR001 is capable of achieving temperatures as high as 50°C.

Since launch, Adveco has deployed hundreds of HR001 heat recovery systems, more than 60 of which are integrated into its bespoke packaged plant rooms recovering refrigerant system waste heat primarily from restaurant freezer units. Running for typically six hours per day, across both gas and electric only systems, weekly heat recovery averages out at 155 kWh/week per site. This saved energy means less overall power demands and therefore reduced emissions. Reducing energy demands also has the bonus of reducing operational costs. With the HR001 requiring a very small electrical input to run the two pumps, considerable savings are achievable with return on investment in as little as three and a half years. For organisations with large-scale freezer/chiller requirements, those savings can be notable, with one customer reclaiming this ‘free heat’ with energy savings to the tune of £55,000 per annum across the business.

Heat recovery presents a simple option for organisations seeking to reduce the energy demands of their buildings by addressing existing waste. It is a proactive undertaking that is relatively easy to implement for both new and existing systems as chiller and freezer circuits remain independent of the heating loop. Crucially though, the ability of each box to recover close to 6,000 kWh of wasted heat annually represents an all-important active investment in reducing energy demands and resultant emissions from building stock.

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