Domestic Hot Water; Temperature Control; Quick Recovery Cylinders - Grant Aerona 290 Installation & Operating Instructions Manual

5 DOMESTIC HOT WATER

5.1

TEMPERATURE CONTROL

By default, the supplied Grant Aerona Smart Controller will
prioritise any DHW demand that is made. The pump/valve
terminals are de-energised as the DHW terminals are activated.
Once DHW is being provided, the flow temperature will adjust to
the target temperature specified on the Aerona Smart controller
for the DHW cylinder. The heat pump will stop when the cylinder
temperatures reaches the desired target temperature, and should
the temperature of the cylinder fall below the set level within the
scheduled period the heat pump will re-engage.
A DHW demand should not exceed 60 minutes in a single period.
This is to avoid excessive heat loss in the space heating circuit(s).
The supplied Aerona Smart controller allows the user to configure
the demand in 30 minute segments.
In addition, the end user can create a 'Boost' DHW cylinder
demand via Grant Aerona Smart Controller. This 'Boost' will heat
the cylinder to the preset target temperature where it will then
deactivate.
We recommend up to 4 x 1 hour DHW demand periods to be
scheduled in a day with at least a 1 hour gap between them.
! NOTE !
There is no limit to the number of times the Grant Aerona
Smart controller can 'Boost' the DHW cylinder.
The Grant Aerona smart controller can also be configured to aid
the heat pump using the immersion heater in a DHW cylinder
with the use of a Grant Immersion relay. If required, the user can
set temperature and time limits on when the immersion relay will
trigger the immersion of the cylinder in a DHW demand.
5.2

QUICK RECOVERY CYLINDERS

As the water temperature from the heat pump is lower than from
a traditional system using a boiler, a much larger coil is required
inside the cylinder to transfer the heat efficiently.
The Grant range of "Quick Recovery" hot water cylinders are
specifically designed for use with heat pumps.
To ensure that a 5 to 8K temperature difference is maintained
between the cylinder flow and return, the correct Grant UK Quick
Recovery cylinder must be selected to match the heat pump
output.
Failure to use the correct cylinder can result in a reduced heat
transfer in the cylinder and a lower temperature differential.
5.2.1 CYLINDER CAPACITY
To calculate the minimum cylinder capacity for a dwelling, use the
following formula:
• Minimum cylinder capacity to meet Total daily DHW demand
= (Number of people x 45 litres) + 40 litres
• Where the Number of people (Np) = Number of bedrooms +1
Example:
To calculate the cylinder capacity for a 3-bedroom dwelling:
• Number of people (Np) = Number of bedrooms + 1 = 3+1 = 4
Minimum cylinder capacity
Knowing that the minimum cylinder capacity to satisfy the total
daily DHW demand is 220 litres, choose the smallest cylinder
that has at least this capacity, i.e. 250 litre cylinder, product code
QRSC250.
Page 28
=
(Np x 45) + 40 litres
=
(4 x 45) +40
=
220 litres
5.2.2 REHEAT TIMES
To calculate the reheat time, specific information must be
available:
• The water volume of the cylinder to be heated
• The specific heat capacity of water
• The starting temperature of the water in the cylinder
• The expected final temperature of the water in the cylinder
• The nominal output of the heat pump being installed
Example:
To calculate the reheat time of a 210 litres cylinder to raise the
water temperature from 30°C to 50°C (preferably within one hour
or so) using an HPR29065 heat pump with an output of 6.1kW at
-3°C ambient when delivering a 60°C flow temperature.
What do we know?
• Cylinder volume (V) = 210 litres
• The specific heat capacity of water (c) = 4.182 kJ/kg°C
• The starting temperature of the water = 30°C
• The expected final temperature of the water = 50°C
• Temperature rise (ΔT) = 50°C - 30°C = 20°C
• Density of water (ρ) = 1kg/litre
• Heat pump nominal output (P) = 6.1kW.
To convert kW to kJ/min, multiply by 60.
6.1 x 60 = 366kJ/min
The equation used is:
Reheat V x ρ x c x ΔT
=
Reheat
Time
Time
Reheat 210 x 1 x 4.182 x 20
=
Time
=
47.99 min ≈ 48 minutes
Table 5-1: Hot water cylinder approximate reheat times from
30°C to 50°C (at -3°C outdoor ambient temperature and 60°C
flow temperature).
Heat pump Heat pump
model Output (kW)
HPR2904 3.6
HPR29065 6.1
HPR2909 8.6
HPR29012 11.6
HPR290155 15.1
! NOTE !
Reheat times are an estimate only and should not be taken
as an exact time period. We recommend that you allow 60
minutes when in domestic hot water mode.
Section 5: Domestic Hot Water
V x ρ x c x ΔT
=
P
P
366
HW Cylinder Approx. Reheat
Volume (litres) Time (minutes)
150 58
180 70
210 81
250 97
300 116
150 34
180 41
210 48
250 57
300 69
150 24
180 29
210 34
250 41
300 49
150 18
180 22
210 25
250 30
300 36
150 14
180 17
210 19
250 23
300 28