Nandos Craigleith: a COOL update to the Dext system

– Dext doubles up in Edinburgh, offering heating e cooling.

The recently completed Nandos restaurant at Craigleith utilises Dex Termico as its primary heating source, in conjunction with a Daikin water-to-water heat pump.

As you’d expect, this provides hot water and space heating using heat recovered from cooking processes and such.

As with 400+ other Nandos restaurants across the UK, hot water is also generated from the DexTherm splashback panel behind the chargrill.

Secondary heating is provided via a Daikin Air Source heat pump when cooking and service are not operational.

What’s new and exciting about the Dext set-up at Craigleith is that we have been able to provide FREE cooling. 

In fact our Dex Termico system is the main source of cooling.

Dext has incorporated this functionality into the design, and the system can be used to lower the air temperature within the building if ambient air temperatures are suitable.
Again, the Daikin Air Source Heat Pump is in place as a secondary cooling source to ensure consistent provision.

At Craigleith during recent warm periods the internal space got to +25°C with an ambient of 23°C, normally these temperatures activate mechanical cooling (using energy to power cooling). What we found, and what was reported from the manager, is that internal comfort at this temperature was satisfactory for customers and staff. This was achieved by increasing the fresh air supply which delivered additional air changes, offering even better indoor air quality.

The combined system means that fewer refrigerants are used at Craigleith compared to other restaurants.

Controlling Craigleith…

With years of experience observing conventional HVAC systems, Dext ensured Craigleith was designed to thoroughly optimise the flow of incoming and outgoing airstreams.

The primary goal is to always to enhance energy efficiency in conditioning restaurant spaces while maintaining the safe operation of air supply and extraction in cooking areas.

At Craigleith, the supply air is split into two separate air streams:

The first serves the dining space, and back of house areas such as office, toilets, staff rooms.

This supply is controlled to keep an internal temperature in the dining area of around 18-21°C in winter and summer.

(18-21°C is widely considered industry standard. With our monitoring and controlling of the system, and in conversation with Nando’s staff we are finding comfort levels within slightly higher temperatures, as mentioned above.)

The second air stream serves the cooking areas, to provide the air for combustion and to allow the canopies to function correctly.

This supply is controlled in winter to keep to a minimum temperature of 16°C.

Supply one utilises a recirculation system, where the DexThermic control system uses motorised dampers to either recirculate the air within the building or mix this with fresh air from outside.

The system also serves the over-door heater, and the cold feed to the hot water system.

The DexThermic system monitors much more than a standard HVAC thanks to our partnership with Siemens.

• It measures the airflow and temperatures within both supplies, allowing us to control the temperatures and calculate the energy inputs required to condition these airstreams.
• It measures the fluid flows and temperatures within the system to validate the energy calculations.
• It measures the electrical energy inputs to both the DexThermic internal skid, and Daikin ASHP.
• It utilises a Siemens Indoor Air Quality sensor that constantly samples the air in the space and compares it with a number of key parameters of Air Quality according to Internationally agreed Standards. 
• It monitors both heat pumps for operational data, and utilises simple digital IO, as well as Modbus connection for system optimisation.

Going forward:

Craigleith will work as a heating / cooling case study, providing exact data about how much heating is required, how much cooling is required, and how much ventilation is required for a restaurant the size of Craigleith.

Nando’s can continue to move away from direct electric and gas heating and take further advantage of heat recovery and heat pump technology.