Low Temperature Hot Water

Published Date: 02 Nov 2017

The Hot Water Supply is served from a primary hot water circuit heated by waste heat from the CCHP engine. This will be backed up by energy efficient condensing boilers for time when the CCHP is down for maintainance. The primary circuit then feeds a calorifier where a heat exchange process begins with mains cold water which is supplied to the calorifier. The mains cold water is then heated and stored at minimum of 60°C this reduces the risk of bacterial growth and other water borne diseases. The water is then conveyed to the system through copper pipework. The system may require heat maintenance tape on the pipework to keep the temperature over 50°C when supplied to the outlets. The outlets will be mixing valves with a sensor to conserve water consumption. The water temperature required at the outlet is around 42°C.

6.4.2 Low Temperature Hot Water

The LTHW systems will be supplied by a primary LTHW circuit that will incorporate a main heat exchanger to use waste heat from the CCHP system. The primary circuit will also be fed by energy efficient condensing boilers for times when more heat than the CCHP can provide is required, or when the CCHP is unavailabele due to maintainance. The secondary LTHW circuits will consist of an AHU constant temperature system which will serve the heating coils of the AHU’s. The LTHW circuits will utilise Variable Speed Drives for the pumps and intelligent two port valve system that incorporates heat meters so that energy usage can be recorded. These valves are called Dynamx valves and are available from Belparts who are a Dutch company.

These valves are pressure independent control valves that can be remotely commissioned. They can optimise flow to the AHU’s and will therefore reduce energy usage when compared with conventional valves. The valve measures heat and flow and as such they can be used as an energy meter (see figure 17). This set up will reduce commissioning time of the LTHW as the valves can be commissioned remotely by the BMS system. It also allows simple re-commissioning should the owners decide to alter the room functions in the clinic. As all that is required is reprogramming of the valve, which can also be done remotely.

Figure Belparts Dynamx valve which can be used as an energy meter.

6.5 Cooling

6.5.1 Chilled Water

The Chilled Water systems will be supplied by a primary Chilled Water circuit. The cooling base load will be met by the absorption chiller which is part of the CCHP package. The system will also require back up cooling to meet higher demand periods as well as providing full cooling when the absorption chiller is inactive during maintenance periods. This will be achieved by using energy efficient chillers. The secondary Chilled Water circuits will consist of an AHU constant temperature system which will serve the cooling coil of the AHU’s. The Chilled Water circuits will utilise Variable Speed Drives for the pumps, intelligent two port valve system, differential pressure controllers, which will be the same type as fitted to the LTHW system. This set up will reduce installation time and commissioning time of the Chilled Water.

6.5.2 Chillers

As the project has different uses, occupation times and varying levels of occupancy, there will be different cooling capacity demands throughout the day. It is proposed to use multiple chillers with different capacities to cope with the different cooling loads required. This will offer better control of variable loads than either a single or equally sized chillers. The chillers will be sized to deal with a base load and increments of a variable load. A control strategy with suitable sequencing can achieve better energy efficiency than a single chiller installation would provide. The chillers will be of the turbo core compressors. The reason behind this proposal is that this offers more operational flexibility, some standby capacity and it is less disruptive when maintenance issues arise.

The reciprocating compressor would not give you a large amount of capacity control as you would get from a screw compressor or turbo core compressors for example

In common situations you would typically have a 2-compressor 2 circuit machine which would only be able to operate the machine in stages by turning on/off one compressor at a time when the load has been met. In this case your running costs would be very high as with a part wind soft start configuration each compressor would draw approximately 200 amps each time starting up.

With a screw compressor you may have just 1 compressor 2 circuit machine where you have more control of the compressor its self when the compressor starts up it will start unloaded to reduce the starting current but would still be as high or higher as the reciprocating compressor.

Then it would start loading the compressor up opening the loading solenoid vales from 25%, 50%, 75% and 100% and would be consuming a large amount of energy.

The turbo core compressor in plan terms is a large invert driven compressor so that at any point from 1% to 100% the correct amount of power and energy is being used at the right time.

The starting current is only 2 amps compared to the 200 amps of the other types of compressor, which in its self would be a large amount of energy and cost savings over a year’s period.

Turbo core compressor:

Choosing between an air cooled condenser or a water cooled condenser?

Water cooled condensers are more efficient but with all the additional plant which would be required and maintained the costs would far out way the benefits which is why the design team has chosen the air cooled condenser to use as there is also the amount of space in which is available for the specific units to be installed in.

The design team has chosen to use the Tech Turbo core air cooled water chiller for this project because:

In 2006 our industry was/now is faced with tougher energy efficiency standards. A combination of EU directive 2002/91/EC and Part L of the UK Building Regulations (in itself a response to the Government Energy White Paper – Our Energy Future Creating a Low Carbon Economy), has ensured that this time around higher efficiency standards are here to stay.

The above R134A air cooled water chiller with turbo coiled compressors and electronic expansion valves with flooded evaporator would be used in a chilled water system which would ideally suit our project because it could maintain a chilled water set point of 6 degrees and supply chilled water and a return of 12°C The condenser coils are suitable for high ambient use of 44°C

As per the F Gas regulation refrigerant leak detection will be installed in the compressor chamber housing and be linked to the main control panel to indicate refrigerant leakage to the Building management system.

Smoke Extract

The smoke extract system will be designed so that it complies with Part B (Fire Safety) of the Building Regulations. There are a number of options available which include; de-pressurisation, pressurisation, separate smoke and ventilation system or a combined smoke and ventilation system.

All of these systems require dedicated smoke extract fans, however the combined system negates the need for extra ductwork. This will save space in the risers as well as reducing the cost of the installation. A combined system utilises the main riser ductwork of the ventilation system, in the event of a fire the ductwork that provides extract in normal mode of operation will be closed by means of Motorised Smoke Fire Dampers (MSFD’s) positioned near the fans, and the smoke extract ……….

1st Floor Corridor Pressurisation

The first floor corridor will be fitted with a Colt stairwell pressurisation package. The reason for pressurising the corridor is to maintain a positive pressure in relation to the isolation rooms.

This type of system has a variable speed fan; the pressure differential between the corridor and the isolation rooms is controlled by means of pressure transducers which send an electrical signal to the fan speed controller in order to maintain a constant pressure when doors to the stair well are opened. The stairwell pressurisation system operates in a fire scenario only and is passive in normal operation.

Toilet Extract Ventilation System

The toilet extract ventilation system will be by a ductwork distribution system connected to a twin fan unit for continuous extract. An extract rate of between 10 – 12 air changes will be required. Local authorities require that the extract fans must be duplicated with arrangements for an automatic changeover in the event of failure of a fan. The toilets will be served by a dedicated AHU, which will be located on the roof.

The toilets must be depressurised so as to prevent unwanted odours from escaping into the building. This will require a higher volumetric extract rate than the fresh air volumetric flow rate.

Kitchen Ventilation

The restaurant kitchen extract ventilation is required for the removal of odours and smoke produced by cooking. The air change requirements need to be high to prevent the spread of odours into the dining room and other areas. An air change of a minimum of 30 air changes will be required. The kitchen supply ventilation will have a volumetric flow rate of 15% less than the extract volumetric flow rate to create a negative pressure in the area, which will prevent the egress of odours into the dining room and other areas.

The Air Handling Units used for these systems will incorporate a heat recovery system to use some of the extracted heat from the kitchen to heat the supply air serving the kitchen area. This will save some energy in the heating of the supply air for the kitchen area. There are two main options to be considered when deciding on a method of extracting air from a kitchen.

Extraction can be either by means of a kitchen hood or through ceiling grilles.

We believe a kitchen hood is the optimal choice for this application as it allows us to reduce the number of air changes. Also it stops smoke and odours spreading through the kitchen.

The extracted air will be filtered for containments before it is discharged to atmosphere, the heat in the discharge air will be recovered by way of a plate heat exchanger. This heat will then be utilised in the supply air serving the canteen. Provisions for the drainage of condensate that will form on the inside of the surfaces will also be made.

Water Services

Install water meter to establish baseline usage.

Use infrared automatic sensor control for the taps so that they cannot be left running when not being used.

Install reduced capacity cisterns; this will reduce flushing volumes.

Given the nature of the building it is highly likely to have a large roof surface area. It will therefore be ideal for implementing a rainwater harvesting system. This water can be used for flushing toilets and irrigation.

BCWS

The mains cold water supply from the water authority is supplied at between 1.4 Bar and 2.7 Bar. Due to the height of the building and the fluctuation of the mains water supply it will be necessary to install a booster pump set.

Fig 15.

BCWS Booster Pump set

We propose to have a storage tank served by the mains cold water from which the boosted cold water pump set will provide cold water to the outlets in the building. The booster pump set will be fitted with a double check valve to stop any backflow and or short circuiting when they are fitted in duplicate. The storage tank will be cleaned and sterilised before the tank is filled with mains water. The tank will be sealed and have access for maintenance purposes and to check the condition of the water. The storage tank will be sized to contain one hour of storage. This is to ensure a quick turnover of water and to safeguard against any stagnation of the water. The tank will be equipped with high and low level float switches and a float operated valve to turn of the mains water supply when the tank is full. The cold water is delivered to the outlets by pipework which has been previously sterilised and drawn through the system to remove the sterilisation agent (this is normally chlorine, but other types of chemical are available including Sanosil® (hydrogen peroxide mixed with silver)). The pipework when delivered to the floor is normally regulated by a pressure regulating valve to around 3.0 Bar this is to control the flow of water and to prevent spillage and water wastage. The installation will be installed to the Water Regulations 1999 and CIBSE Guide G Public Health.

Drainage

There are a number of options for the provision of drainage, the company will maximise the re-use of waste water where possible, and this includes the use of ‘grey water’ and rainwater which are discussed in more detail in the next section of this report. Water which is classed as effluent is termed ‘Black water’. Black water contains faeces, and as such it must be chemically treated before it can be discharged. The disposal of this type of water will be through the existing connections to the main sewer. Due to the fact that rainwater harvesting and re-use of grey water is planned, the existing connection will actually have to deal with less waste water than when the building was previously used. The pipe work that will be used is the OsmaSoil solvent weld plastic pipe system. The employment of this type of system has been chosen specifically to reduce capital costs. We believe that the building has completed its ‘settlement’ period and that there should be no further subsidence and as such plastic solvent welded pipe will be more than satisfactory. The size of the pipework used for the drainage of Black water will be 110mm. All installed drainage will comply with Part H (Drainage and Waste Disposal) of the Building Standards, as well as CIBSE Guide G (chapter 2 Public Health Engineering).

Grey water

Water that has been used for washing purposes in the building is called ‘Grey water’. This grey water can be harvested treated and then reused for the purpose of irrigation and to provide water for flushing the toilets and urinals. The amount of grey water produced by a building of this nature is significant. Collection and re-use of this grey water will involve the installation of an underground septic tank, a natural filter mechanism, a sump pump and associated pipework. This will add additional capital costs; however we believe that using this type of system is not only environmentally friendly, but that this type of system will be beneficial to the client. The benefits of this type of system include;

• Reduction in size and cost of the septic system, as well as extended system lifetime. This is due to the fact that the septic system will only be required to deal with ‘Black water’.

• Reduction in cost of energy and chemicals used, this is due to the reduced amount of wastewater that needs pumping and treatment.

• Reduction in CO2 emissions.