Category: Technical information associated with Armstrong
pressurisation selection boosting selection
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Armstrong
Pressurisation & Boosting Selection
Pressurisation Unit & Expansion Vessel Selection
In order to correctly size pressurisation equipment in LTHW and
Chilled Water Sealed Systems it is necessary to establish certain
information. The answers to the questions below will ensure that the
correct unit is selected when using Armstrong PC selection program,
(copies available on request), or when requesting selection by the sales
department. The information required is as follows:-
1 Where will the pressurisation unit and expansion vessels be installed.
Will the location be a basement, or roof-top plantroom, or somewhere
else?
2 Is there a suitable water supply at this point?
3 What is the static head at the pressurisation unit? i.e. What is the
height from the pressurisation unit to the topmost radiator or service
point above it?
4 What is the boiler/chiller rating?
5 What are the flow and return temperatures?
6 What is the total water content of the system?
7 What size of pipe is being used and therefore what size of air
separator is required?
8 What is the proposed position of the circulating pump in relation to
the boiler/chiller?
9 What is the duty of the circulating pump?
10 What is the maximum allowable pressure, (pressure at which the safety
valve starts to open)?
11 What is the percentage of antifreeze to system volume?
Methods of Supplying the Maximum Probable Simultaneous Demand (MPSD)
with a Booster Set
In the majority of applications a booster unit must provide for the
MPSD. Since this is not normally a continuous requirement, the following
methods of sharing the demand may be considered:-
12 Where the flow rate requirement is small, a two pump unit can have
each pump sized to cater for 100% of the MPSD, one pump acting as the
Duty pump, the other as Support.
13 Alternatively, the two pumps can each be sized to handle 60% of the
MPSD, where the second pump is switched in to cater for the occasions
when peak demand occurs.
14 Where the flow requirement is high, it is more economical to select a
three-pump unit such that the duty of each pump is 50% of the MPSD. Here
the pumps function respectively as Duty, Support and Back-up.
15 A jockey pump with a small capacity can also be added to any of the
above arrangements, which will save energy during low demand periods.
Alternatively, a larger pressure vessel can be supplied to cater for
long periods of low demand, from small draw-off points on the rising
main, e.g. vending machines.
Boosting Pump Selection Chart
6800 Series with SV Pumps
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Armstrong
UK HVAC Sales North
Wenlock Way
Manchester
M12 5JL
Tel: +44 (0)161 223 2223
Fax: +44 (0)161 220 9660
UK HVAC Sales South /Services
21-23 Ormside Way
Holmethorpe Industrial Estate
Redhill
Surrey
RH1 2NT
Tel: +44 (0)1737 378100
Fax: +44 (0)1737 378140
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