This tab allows you to describe the characteristics of the domestic hot water heating systems. This approach is suitable for use in Building Regulations compliance tests, ApacheSim, ASHRAE Loads and CIBSE Loads.
Generator
Data on this tab allows you to describe the characteristics of the domestic hot water heating system associated with the Apache System. These properties are used in UK Building Regulations compliance tests and ApacheSim. Domestic Hot Water (DHW) calculations feature optionally in ASHRAE Loads and CIBSE Loads calculations.
The tab is accessed using the ‘Hot Water’ tab on the Apache Systems dialog. The parameters describing the DHW and solar water heating systems are different for ApacheSim and the UK NCM program SBEM.
DHW demand is calculated from settings on the Room Conditions tab in the Building Template Manager or Space Data.
Is DHW served by ApacheHVAC boiler?
Tick this box if DHW is supplied by the ApacheHVAC system. A single heat source should then be nominated in ApacheHVAC to meet the DHW demand.
Generator type
This setting only applies in VE Compliance. Choose the DHW generator type from the list.
DHW delivery efficiency
The efficiency of the delivery of Domestic Hot Water, expressed as a percentage. Heat is lost from the pipes carrying hot water from the boiler (or other heat generator) to the taps, and the resulting cooling means that a certain volume of water has to be run off before hot water reaches the outlet. The delivery efficiency accounts for this process. If secondary circulation is used the DHW delivery efficiency should be set to 100%, as the pipe heat loss is accounted for elsewhere.
DHW Generator seasonal efficiency (SBEM only)
Accept the default efficiency for the DHW generator or enter manufacturer’s data.
Set Points
Mean cold water inlet temperature
The temperature at which mains water is supplied to the building. Forced to 10°C for NCM. See Para. 51 2010 NCM Modelling Guide.
Hot water supply temperature
The temperature at which hot water is delivered. Forced to 60°C for NCM.
Storage
Is this a storage system?
Tick this box if the hot water system has a storage tank.
Storage volume
The volume of the DHW storage tank. This is used, with the following parameters, to calculate tank losses.
Insulation type
This parameter and the following are alternative ways of specifying the insulation of the tank. The options for ‘Insulation type’ are ‘Uninsulated’, ‘Loose jacket’ and ‘Factory insulated’.
Storage losses
The DHW storage tank loss factor (kWh/l/day).
The following tables from SAP (2005) may be helpful in setting this parameter.
Table 2: Hot water storage loss factor (kWh/(l.day)
|
Insulation thickness (mm)
|
Cylinder loss factor (L) kWh/(l.day)
|
|
Factory insulated cylinder
|
Loose jacket
|
|
0
|
0.1425
|
0.1425
|
|
12
|
0.0394
|
0.0760
|
|
25
|
0.0240
|
0.0516
|
|
35
|
0.0191
|
0.0418
|
|
38
|
0.0181
|
0.0396
|
|
50
|
0.0152
|
0.0330
|
|
80
|
0.0115
|
0.0240
|
|
120
|
0.0094
|
0.0183
|
|
160
|
0.0084
|
0.0152
|
Note: Alternatively the heat loss factor, L, may be calculated for insulation thickness of t mm as follows:
1) Cylinder, loose jacket L = 0.005 + 1.76/(t + 12.8)
2) Cylinder, factory insulated L = 0.005 + 0.55/(t + 4.0)
Table 2a: Volume factor for cylinders and storage combis
|
Volume Vc
|
Volume Factor VF
|
Volume Vc
|
Volume Factor VF
|
|
40
|
1.442
|
180
|
0.874
|
|
60
|
1.259
|
200
|
0.843
|
|
80
|
1.145
|
220
|
0.817
|
|
100
|
1.063
|
240
|
0.794
|
|
120
|
1.000
|
260
|
0.773
|
|
140
|
0.950
|
280
|
0.754
|
|
160
|
0.908
|
|
|
When using the data in Table 2, the loss is to be multiplied by the volume factor.
2) Alternatively, the volume factor can be calculated using the equation
VF = (120 / Vc )1/3
Where:
Vc – volume of cylinder or storage, litres
Secondary Circulation
Does the system have secondary circulation?
Tick this box if the hot water system has secondary circulation. A secondary circulation system pumps water continuously round a circuit connecting the heat source to the outlets to provide instant hot water.
Circulation Losses
The loss factor of the secondary circulation system, per unit length of pipework (W/m).
Loop Length
The length of the secondary circulation system (m).
Pump Power
The rated power of the secondary system pump (kW).
Is there a time switch?
Tick this box to indicate that secondary circulation is turned off when the rooms served by the hot water system are unoccupied.
