1st Floor Corridor Pressurisation Engineering Essay

Published: 2021-07-01 17:50:05
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The first floor corridor will be fitted with a Colt 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 corridor pressurisation system will operate constantly and will ramp up and down to maintain a positive pressure of > 8 Pascal’s . The control of the system is described in section
Kitchen Ventilation
The 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 surrounding 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 high negative pressure in the area, which will prevent the egress of odours into any surrounding areas.
There are two main options to be considered when deciding on a method of extracting air from the kitchen. Extraction can be either by means of a kitchen hood or through ceiling grilles.
A kitchen hood in the case of the hospital is the optimal choice for this application as it allows a reduction 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. Provisions for the drainage of condensate that will form on the inside of the surfaces will also be made.
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; forced extract, 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 supply in normal mode of operation will be closed by means of Motorised Smoke Fire Dampers (MSFD’s) at the air handling units, and the smoke extract fans MSFD will be opened. The smoke will then be extracted from the high level supply grilles. It was not possible to use the extract ductwork as it has been positioned at low levels for reasons outlined in section 7.12 of this report.
6.5 Heating
6.5.1 Domestic Hot Water
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 maintenance. 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.
6.5.2 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 unavailable due to maintenance. 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 17 Belparts Dynamx valve which can be used as an energy meter.
6.6 Cooling
6.6.1 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 circuit 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.
6.6.2 Chillers
An absorption chiller which is a Thermax model LT12C has a cooling capacity of 422kW and a COP of 0.7. It was selected because the size is equivalent to the cooling base load and a vapour compression chiller will supply additional cooling for increments of an increased load.
Figure 18 Monthly cooling loads taken from IES.
The chillers will be of the turbo core compressor type. A control strategy with suitable sequencing will achieve better energy efficiency. The reason behind this proposal is that this offers more operational flexibility, some standby capacity and it is less disruptive when maintenance issues arise. A reciprocating compressor type chiller would not give as much capacity control as can be delivered from a screw compressor or turbo core compressor.
In common situations you would typically have a two compressor two circuit machine which would only be able to operate in stages by turning on or off one compressor at a time when the load has been met. In this case the running costs would be high as with a part wind soft start configuration each compressor would draw a high current each time on start up.
With a screw compressor you may have just 1 compressor 2 circuit machine where you have more control of the compressor itself when the compressor starts up it will start unloaded to reduce the starting current but would still be as high or higher than the reciprocating compressor. It would then start loading the compressor up by opening the loading solenoid vales in 25%, 50%, 75% and 100% increments and would be consuming a large amount of energy as a result.
The turbo core compressor in simple terms is a large inverter 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 much lower than that of the other types of compressor, which in itself equates to a large amount of energy and cost savings over a year’s period.
Water cooled condensers are more efficient and the fact that the air temperature in Chiang Mai is so high means that air cooled condensers would not have a high efficiency. Therefore the chillers will be water cooled and as such a dry air cooler and associated pipework and pumps will be required for the condense water circuit. The chiller has been sized to deal with the peak building load (see table 9) this will ensure full cooling even if the absorption chiller is not operational.
Table 9 Chiller peak load taken from CIBSE plant loads, calculated using IES software.
The chillers selected will be two Airedale model 611chillers which have a cooling capacity of 567kW each this will give a combined capacity of 1134 kW which is enough to meet the peak cooling demand. They would be used in a chilled water system which would meet the requirements of the project because it could maintain a chilled water set point of 7 degrees and supply chilled water and a return of 12°C which is the same as the absorption chiller. The condenser coils as stated will be water cooled and the condenser system will use a dry air cooler to dissipate heat from the condenser water circuit.
The reason that two chillers will be used is that the chillers are more efficient at higher load so efficiency can be maximised by using only one chiller at full load when the cooling demand is lower. The chillers will be in parallel as this will mean that when one of the chillers is not required the pumps will not need to overcome the coil resistance of the non-operational chiller eliminating the additional pressure drop that this would present, and reducing pump energy usage.
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.
6.7 Water Services
6.7.1 Boosted Cold Water and Boosted Rainwater supplies
The mains cold water supply from the water authority is supplied at between 1.4 Bar and 2.7 Bar. Due to layout of the building, water usage and the fluctuation of the mains water supply it will be necessary to install a booster pump set.
It has been decided 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, which is 750 litres. 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.
6.8 Drainage
There are a number of options for the provision of drainage, the company will maximise the re-use of waste water where possible this will be achieved by installing a rainwater harvesting system as discussed in section 5.7.
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 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. It is believed that by constructing proper foundations any subsidence or settlement can be avoided 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).
6.9 Electrical Supply
The incoming electrical supply will consist of two separate electrical mains feeds as this in conjunction with the CCHP electrical supply will provide the clinic will the necessary resilience. If one of the supplies is lost there will be an additional supply to ensure all hospital systems can continue to run, this is the case even when the CCHP is not operating during maintenance periods as shown in Fig 19.
Figure 19 Electrical schematic of incomer configuration.
6.10 Lighting Systems
A glare analysis was undertaken using IES. The first analysis was for the window to determine the daylight glare. As can be seen in figure 20 the analysis was conducted from the patients viewpoint, lying prone on the bed. The analysis was conducted in isolation room 11. The results shows that glare does exist and that an internal blind would be required. This will not affect the solar gains into the room.
Figure 20 Daylighting glare analysis results
Following on from the initial analysis a second study was under taken with lighting on the ceiling. As can be seen from the results of this analysis, see figure 21, the lighting would cause the patient discomfort from glare if the lighting system were to be installed on the ceiling. Given that the patient is expected to be facing the ceiling most of the time it is apparent from the analysis conducted that the lighting system cannot be installed in this configuration.
Figure 21 Glare analysis of daylighting and ceiling lighting system.
In order to overcome the problem of glare from the lighting system a package solution was found by searching through products offered by specialist manufacturers.
It is believed that given their experience in the hospital lighting field that the lighting solutions offered by Thorn would be most suitable. A wall mounted luminaire system such as that shown in figure 22 would solve the problems of lighting glare whilst also ensure adequate standards of lighting are provided. The system has both uplighting
Figure 22 Thorn wall mounted lighting solution.
7.0 Literature Review
7.1 CCHP Fuel Selection
CHP engines can run on a large variety of fuels. The selection of fuels to use on the project is a highly contentious issue. A large number of factors have to be considered before deciding which fuel is the optimum type to be used by the CCHP system. The issues can be summarised into the following categories.
• Fuel Cost.
• Fuel availability.
• Fuel should qualify for exemption from climate change levy (CCL).
• Fuel should be produced ethically.
• Fuel must use minimal fossil fuel for its production.
• Fuel should be sourced as locally as possible to reduce CO2 production from transportation.
7.1.1 Fuel cost
Fuel costs must be considered for the lifetime of the CCHP installation. The cost of fuel is spiralling as demand increases. Naturally the client will want the cheapest option available, however by researching expected fuel increases it may prove that the most cost effective solution right now may prove to be the most expensive solution in ten or twenty years time.
7.1.2 Fuel availability
There are new developments in fuel technology such as production of biofuel from algae and the development of green petrol, Scientists at University of Massachusetts-Amherst in America have created a green fuel that has been christened ‘grassoline’ which has properties similar to that of petrol however it has next to zero carbon footprint. Whilst the development of these fuels is of significant importance and will undoubtedly help to solve the energy crisis, they are not yet readily available to consumers; algae biofuel is currently too expensive to be viable. Fuel must be readily available in enough quantity so that continuous supply will not be in jeopardy.
7.1.3 Qualification of fuel for CCL exemption
A fuel will qualify for CCL exemption if it is renewable. Thus fossil fuel is not an option for the clinic CCHP engine.
7.1.4 Fuel should be produced ethically
Some biofuels are now being cultivated on land that was once forest and the push to increase biofuel production in countries such as Brazil and Indonesia can lead to deforestation . This not only endangers wildlife by removing their habitat but also the burning of the chopped down trees releases their stored carbon as carbon dioxide exasperating the problem of global warming. Additionally some countries are actually reducing the amount of land they use for growing food crops so that biofuel producing feed stock can be grown instead. Whilst this increases revenues for the farmers it reduces the countries food stocks and pushes up food costs . In a bid to avoid exasperating these problems checks must be conducted to ensure the biofuel production is not having these detrimental effects.
7.1.5 Fuel must use minimal fossil fuel for its production
Different biofuels use different amounts of fossil fuel for their production. A biofuel does not grow as a ready to use product. It must be refined and this uses energy. The amount of energy it takes depends on how easy it is to grow, i.e. use of fertilizers, difficulty harvesting etc. It also depends on how easily it can be refined to a useable fuel.
7.1.6 Fuel should be sourced as locally as possible to reduce transportation CO2 production
It’s all very well having a cheap source of biofuel that is ethically produced and in plentiful supply, but if it needs to be transported over great distances then some of the carbon dioxide reduction benefits will be lost. In order to maximise the CO2 reduction the fuel should be sourced locally. This means that it should preferably be produced in Thailand if possible.
7.1.7 Which Fuel to use?
There is a multitude of fuel choices and they can be broken down into four specific groups
1st Generation
(Derived from Sugar Starch and Vegetable Oil)
• Bio-alcohols
• Bio-Diesel
• Renewable Diesel
• Vegetable Oil
• Bio-ethers
• Bio-gas
• Syngas
• Solid Bio-fuels
2nd Generation
(Derived from non crop foods)
• Waste Biomass
• Jatropha Curacas
3rd Generation
(Bio-fuel from Algae)
• Ethanol from Living Algae
• Distillates
4th Generation
(Other processes under development or under further research)
• Green Diesel
• Green Petrol
• Green Aviation Fuel
As discussed previously there are strict criteria to be met in choosing a fuel for the clinic. At the present time 3rd generation fuels are too expensive and 4th generation fuels have a lack of availability. They have been included in the research because whilst they may not be affordable or available at this moment in time they may be in the future. Their use in the CCHP engine could be possible. The process for accommodating and using these fuels in the CCHP would require only slight modifications to the engine which could be conducted during pre-planned maintenance thereby reducing costs.
Therefore for this installation 3 different types of fuels, from 1st and 2nd generation types will be investigated. The fuels to be investigated are;
• Palm Oil (1st Generation)
• Soya Bean Oil (1st Generation)
• Jatropha Oil (2nd Generation)
7.1.8 Cost Comparison
The rate per barrel in US Dollars is shown in figure 23 the costs were obtained online .
Figure 23 Cost of fuel per barrel
As can be seen soya oil does not score as highly as palm oil or jatropha oil, both of which are roughly the same price. The future price of all three is not as volatile as fossil fuels. It is believed that with better refining techniques and increased yields that the price of all three fuels will not deviate much. It is possible that the cost could even be reduced due to competition between suppliers.
7.1.9 Fuel availability comparison
Palm oil and soya oil are readily available in Thailand as is jatropha oil According to Green Energy Group Thailand will become a leading exporter of jatropha in the next decade .
7.1.10 Exemption from CCL
All three fuels qualify for CCL exemption.
7.1.11 Fuel should be produced ethically
Palm oil plantations take 4 years to begin production of oil whereas jatropha plantations will produce oil after 6-9 months. Both soya and palm oil need fertile arable soil in order to grow. Jatropha can grow on marginal land and as such would not be displacing food crops, it must be noted that yields will be lower on marginal land, but it can grow and produce a usable yield.
7.1.12 Amount of fossil fuel used for biofuel production
The amount of energy that goes into producing a useable biofuel is different for each of the fuels. The energy produced from the fuel divided by the energy input required to produce it is called the energy balance. The energy balance for the three different fuels is as follows;
Jatropha oil = 4.6
Soya oil = 1.2 – 3.6 (dependent on extraction technique)
Palm oil = 4.8
The higher the energy balance figure the lower the amount of fossil fuel required for cultivation and refining.
7.1.13 Reduction of CO2 production from transportation
Chiang Mai will be one of the main production centers for refined jatropha biofuel ; this will reduce not only transportation costs but also reduce CO2 emissions resulting from long distance transportation. Palm oil and soya oil are not grown in Chiang Mai and therefore this would mean additional CO2 production and transportation costs.
7.1.14 Decision Matrix for Fuels to be used by the Clinic CCHP Engine
Given all of the factors discussed a decision matrix was used to select the fuel to be used and is shown below in figure 24.
Figure 24 Decision matrix for fuel selection.
Figure 25 Fuel decision matrix in graphical format.
The fuel selected is Jatropha oil, regular reviews taking into account the factors outlined in section 7.1 must be undertaken to offer assurances to the client that the selected fuel remains the optimal choice in future.
7.2 Preventing Airborne Transmission of Diseases from Isolation Rooms
The overriding design feature of this hospital is the ability to prevent the transmission of airborne transmission of disease. This is facilitated in a number of ways in isolation rooms such as;
• Room air dilution by having a large number of air changes.
• Maintaining pressure regimes to prevent airflow to adjoining areas.
• Maintaining air flow regimes.
• Ensuring proper filtering of discharge air.
• Ensuring that discharges are located in the correct place.
• Room visitors and nurses to wear masks and gloves.
7.2.1 Room Air Dilution, Flow Regimes and Pressure Regimes.
Airborne disease is transmitted through moisture droplets that are suspended in the air and that contain pathogens. These droplets can be either large or small large droplets." Generally large droplets have a mass median aerodynamic diameter (MMAD) of >10 micrometers - µm); and small particles have a MMAD <10 µm and are sometimes termed droplet nuclei" .
Droplet nuclei can remain suspended in the air for hours and there must be removed by changing the air in the room. This is accomplished by forcing fresh air into the space and then extracting it which gradually changes all of the air in the room. How well this is accomplished depends on the dynamics of the air flow in the room. In order to establish the optimum flow regime the supply and extract terminal positions size and number will need to be researched to identify which configuration works the best. For example one large extract above the patient may be better than 4 smaller offset grilles. The issue is that you may have air flowing into the room and then being extracted without actually circulating. This would mean that any droplets would remain suspended in the room for longer increasing the chances that someone could be infected.
In order to ensure the rooms were designed to provide optimal air movement and distribution within the space a computational fluid dynamics (CFD) study was undertaken. This was done in 2 ways, firstly the mean age of the air in the room was examined and secondly particle tracking from the mouth area of the patient was conducted. The research was also conducted in two sections;
1. With low level supply diffuser and high level extract.
2. With High level Supply diffuser and low level extract.
The room was populated by 2 people to represent the patient and carer. The patient was placed in a hospital bed in the prone position to replicate what would be the expected normal conditions for the room with regards to heat sources etc. The objective of the CFD modelling was to evaluate the effectiveness of the flow regime by measuring the age of the air in the room.
7.2.2 CFD Study Section 1
Figure 26 below shows the mean age of air with the supply at low level and the extract at high level. The reason for this configuration is that it was expected that by supplying air at low level it will pick up heat more effectively and the thermal plume created would help to expedite the extraction of contaminated air at high level.
Figure 26 CFD study section 1: Mean age of air with low level supply and high level extract.
As can be seen from figure 26 the mean age of air around the patient is up to 4 minutes old which indicates poor air distribution. This is inadequate and will allow the build-up of droplet nuclei which will in turn increase the possibility of airborne transmission, additionally the air in the areas around the patient’s bed show poor results.
A particle tracking study was then conducted to check the actual path of droplet nuclei emitted from the patient. By placing the source of the particle above the patient’s mouth the movement of the emitted droplet nuclei could be demonstrated. As can be seen in figure 27 below the emitted droplet nuclei will flow down the bed at patient level and then be transported though the air to the extract grille. What is important is the area that the droplets pass through. When crossed referenced with the mean air age in figure 26 it can be assumed that the droplets will remain suspended in the air for up to 6 minutes.
Figure 27 CFD study section 1: Particle tracking with low level supply and high level extract.
The results of the section 1 CFD analysis indicted that the ductwork terminal placement was inadequate. The mean age of the air was too great, the distance travelled and time taken to travel that distance was unacceptable.
Further analysis was under taken by changing the grille type position and number, however the results were much the same and in most cases not as good. It was decided following this analysis that the positioning of the supply terminals at low level would not produce the required results. In fact it could be assumed that this configuration actually exacerbates the situation by spreading the droplet nuclei over a wider area actually increasing the chances of airborne transmission to carers and visitors.
7.2.3 CFD Study Section 2
After conducting studies on grille velocities and positioning it was decided to place the extract terminals at low level behind the patient. This configuration seemed to work better than all others that were attempted. Figure 28 below shows the mean age of air with the supply at high level and the extract at low level. It can been seen that the age of the air around the patient is a matter of seconds old rather than minutes old as was seen in study section 1. These results were far better and were deemed to be optimal for this size and type of room. It is noted that near the door area there is less air movement. This is not however a bad thing as the room will have a negative pressure in relation to the adjacent corridor and that means there will be some infiltration through the door. That was not taken into account on this study due to the limitations of the IES software when it comes to complex CFD modelling using differential pressures from multiple adjacencies. What is clear however is that the flow of air around the patient should help to prevent any droplet nuclei from entering this area of the room.
Figure 28 CFD study section 2: Mean age of air with high level supply and low level extract.
A particle tracking study was then conducted to check the actual path of droplet nuclei emitted from the patient. By again placing the source of the particle above the patient’s mouth the movement of the emitted droplet nuclei could be demonstrated. As can be seen in figure 29 the emitted droplet nuclei will flow down the back of the bedstead straight to the extract grille at low level. The droplets will not be suspended in the air for very long at all possibly only for less than a minute. Again the results from the particle tracking show a vast improvement on the previous study.
Figure 29 CFD study section 2: Particle tracking with High level supply and low level extract.
The results of the section 2 CFD analysis indicted that the ductwork terminal placement was optimal. The mean age of the air was very low, the distance travelled and time taken to travel that distance was desirable as it minimised the distance travelled by the particle and prevented it from being moved around the room.
7.2.4 Optimal Grille configuration
The CFD analysis conducted proved that location of the terminals is absolutely critical to creating a safe and hygienic environment. It showed that droplet nuclei can be controlled and prevented from lingering around the patient or pervading the room in the room. As discussed previously a number of different options were trialed and the optimal configuration was as follows;
SUPPLY
One 400mm x 400 mm 4 way supply diffuser supplying 350 L/s of fresh air conditioned to 20 oC at a velocity of 5.68 m/s ceiling mounted above the area between the end of the patient bed and the wall.
EXTRACT
Two 200mm x 300mm extract grilles extracting 185 L/s of contaminated air each at a velocity of 3.08 m/s floor mounted at either side of the bed.
The positions of the terminals can be seen in figure 30.
There was some concern that the supply velocity and positioning of the supply grille may cause discomfort to the patient as it could feel draughty. A check was therefore conducted to ensure velocities near the patient were at and acceptable level. Figure 30 shows that the concerns were unfounded and that there was no problem of high velocity air passing onto or near the patient. An air velocity of between 0.1 and 0.45 m/s was deemed to be within comfort range.

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