- Balanced hot and cold water pressures
- Improved shower performance
- Less pipework and no storage cistern
- Reduced risk of frost damage to system
- Saving on installation time and costs
- High resistance corrosion
- Excellent heat transfer capability
- Allows the use of a wider range of modern tap fittings and showers
- High efficiency insulation
- Flexibility of vessel siting and hence system design
Fig 1. Shows a typical unvented hot water system
- Water Services & Utilities break-down
- Cold Water Storage
When designing the water storage for domestic, commercial and industrial accommodation the unit rates recommended for a number of fittings are listed in Table 2.2 (abstract from Cibse Guide G: Public Health Engineering- 2.4.3.1)
From the table below I have came to the desired amount of fittings and the recommended water storage requirements for the project:
If the expected occupancy of the building is not known, the engineer may use the requirements of the Offices, Shops and Railway Premises Act 1963, to estimate the likely building occupancy, where a general allowance is given of 10m² per person of actual working floor space excluding the floor area occupied by such items as toilet facilities, staircases, passages (Extract from Cibse Guide G- 2.4.4 Occupancy).
Although the drawings provided of the floor area aren’t to scale, the dealership is 130mm by 130mm, I have therefore assumed this to be 13m by 13m giving a ground floor total floor area of 169m² (this figure will be used further along in Part 3.4), and first floor area of 4m by 13m equalling 52m². This then gives a total floor area before deductions for toilet facilities and unoccupied space of 221m².
The deductions are as follows- (Ground Floor) 24m² for the Store, 4m² Corridor, 4m² Customer Toilets, 8m² Plant Room, (First Floor) 6m² Lift Area, 8m² Shower and Staff Toilets, and 4m² Record Stores.
Therefore the overall workable floor area after the deductions is 163m², then rounding this up and allowing and additional 3 people for car salesmen who work on the forecourt as well as an average of 5 customers in the dealership at any one time, I have assumed the dealership to have 20 employees and 5 customer giving a total of 25 people.
- Hot Water Storage
As previously discussed in the introduction my system of choice is an unvented hot water storage system. From Cibse Guide G: Public Health Engineering I can determine the daily hot water demand per occupant within the dealership. This is information is presented in Table 2.10:
I have made the assumptions that almost half the employees are classed as working in a factory (i.e.: in the Bodywork repair, Service and MOT area) and the other half of the employees and customers are classed as being in an office.
With the compiled information I have then determined the total daily storage of hot water required, see the table below for details:
- Plant Sizing (including Boiler Rating)
By referring to Cibse Guide G: Public Health Engineering, section 2.7.3.2 I can determine the rating and size of plant for my hot and cold water demand by comparing it against the plant sizing curves.
By using an Off-peak Tariff I can determine the following:
My dealership has offices, a workshop consisting of a showroom and services within the premises with 20 staff and 5 customers at any one time requiring a hot water heater to supply water at 55ºC to wash basins, sinks and hose outlets within the workshop area.
- From the table above I have established that I require a two-hour recovery period.
-
From the office curve (a) in Figure 2.16:
qu= 0.04(kW/person)
νu= 1.2(L/person)
- Adjust the upper limit rating:
qu= qu (y-a)
qu= 0.04x [(55-10)÷(65-10)]= 0.033 kW/person
-
From the office curve (b) in Figure 2.16 and assuming a 40% on-peak rate:
q1= 0.0325 kW/person
ν1= 3.3 L/person
- Using the number of people applicable:
ν1= 3.3 x 25 = 82.5 = 83 (1)
νu= 1.2 x 25 = 30 (1)
q1= 0.0325 x 25 = 0.8125 = 0.813 kW
qu= 0.033 x 25 = 0.825 = 0.83 kW
- Assume system heat loss, L, has been calculated as 0.166 kW (20% of 0.83kW):
Qu’= 0.83 + 0.166 = 0.996 = 1.0 kW
- For a 10-hour day (9am-7pm):
(Where E is the equivalent volume (1); L is the rate of the system heat loss (kW); n is the period of operation of system (h). Also: 4.2 is the specific heat of water in kJ/kg K, 3600 is the number of seconds in an hour)
E = Ln3600
4.2(y-a)
E = 0.166 x 10 x 3600 = 31.619 = 32 Litres
4.2 x (55-10)
- Calculating the increase in V
I = (100 – P) x E
100
(Where I is the increase in hot water storage capacity (1); P is the annual on-peak proportion selected (40%).
I = (100-40) x 32 = 19.2 = 20 Litres
100
V1’ = V + I
V1’ = 83 + 20 = 103 Litres
-
Calculate the adjustment necessary to Q1:
Q1’ = Q1 + [1 x Q1]
V1
(Where Q1’ is the adjusted lower element rating (kW)
Q1’ = 0.813 + [20 x 0.813] = 1.0089 = 1.01 kW
83
- Add 25% allowance for mixing of incoming cold water with hot water. Final hot water storage capacity is:
V1’ + E = 103 + 32 = 135 (l)
From the information collated above I now need a boiler with a rating of:
- 1.01 kW and a hot water storage capacity of 135 Litres.
- Sanitary Accommodation, Pipework & Drainage requirements
- Assessment of Sanitary Accommodation
This section covers those aspects of sanitation, and foul and surface water disposal in the immediate car dealership curtilage. You will find below a schedule of sanitary accommodation and other water users, (which are identified on the attached drawings) as well as the flow rates required.
From table 3.2 from the Cibse Guide G- 3.3 Assessment of sanitary accommodation we can establish the recommended minimum number of water closets (WC’s), urinals and baths:
- Foul water Drainage
Foul water is the waste from sanitary conveniences and other sanitary appliances, and also water which has been used for cooking or washing.
The drainage system should comprise the minimum work necessary to carry foul water away from a building quickly, quietly, free of nuisance or risk to health, and should also prevent the escape of foul air into the building.
The fumes in foul water systems contain a ‘cocktail’ of gases which can be potentially lethal. To prevent fumes from the drainage system entering a building, a trap with an adequate water seal should be provided on each sanitary appliance. The discharge from appliances produce fluctuations and the drainage system should be designed to retain adequate water seals in all traps under normal working conditions.
From Table 3.9 of Cibse Guide G- 3.4.3 Assessment of Flows we can determine the recommended discharge data:
Having established a practical scale of discharge units the probability table (found in Cibse Guide G: Public Health Engineering, Table 3.9) may now be transposed to convert directly the totals of discharge units into design flow rates as listed below.
- Vertical Discharge Pipes (Stacks)
With regards to the two sets of stacks (2 for grey water (unvented) and 2 for Black water (vented)) as illustrated in the drawings attached there are set criteria’s which will determine the size (diameter) of the plastic discharge pipe.
The vertical stacks collect discharges from the branch discharge pipes. These pipes are generally required to be vented. In the case of the car dealership the stacks (also known as ventilating pipes) will from the ground floor and out through the roof where they will be vented to the atmosphere.
From Table 3.14 in Cibse Guide G it can be shown below that the approximate capacity of stacks (1/s) with diameter 150mm is 22.7, and the approximate number of discharge units is 5500. Compare this with my totals above for WC (2400 max capacity of stacks (1/s) and 15.8 discharge units) and you will that an 150mm diameter is vertical pipe is compliant but the 125mm isn’t compliant with the approx capacity of stacks (1/s).
- Surface & Below-Ground Drainage Systems
Surface water is the water that affects a building or its surround as a result of rainfall, which has been illustrated by means of storm drains in the attached drawings but for the purpose of this coursework gutters haven’t been included.
The design for the provision of storm water drainage depends on an assessment of the likely worst case condition for the intensity of rainfall of the site and buildings.
For design purposes, in the UK the rate is 75mm/h, which is based upon a 50-year worst case scenario. A lower rate of 50mm/h may be taken for a 20-year worst case scenario.
To calculate rainfall run-off from any area the Wallingford ‘Rational’ Method can be adopted. The Lloyds-Davies formula associated with this method can be simplified and given as:
Q = 0.021 A P
(Where A is the area (m²), P is the impermeability factor and the rainfall intensity is 75mm/h. The impermeability factor is a measure of the proportion of the total rainfall which will be taken by the storm water system compared with the total which has fallen.)
A = 173mm x 173mm = 299.29mm – 169mm (as previously calculated for the floor area of the dealership in part 2.1) = 130.29m²
Total rainfall run-off equals:
-
Q = 0.021 x 130.29 x 0.75 (given in Table 3.15) = 2.052 = 2.1 (l/s)
From the total rainfall run-off calculated I could then go onto work out the flow rate of the below-ground drainage pipework and finally derive the size of drainage pipe required for the dealership.
- Bibliography
- Cibse Guide G : Public health Engineering
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