Systems - HOWATHERM

HP-WRG SYSTEM
HYDROPLUS SYSTEM
Thermodynamic heat recovery with > 99 % counter flow
Technical information about
high-performance cycle compound heat recovery systems
based on countercurrent heat exchangers

2
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Heat recovery in
air handling units
HOWATHERM Klimatechnik has been specializing
for nearly 30 years in the development
and production of efficient
systems for air handling applications to
create and maintain comfortable indoor
atmosphere for people.
For pre-heating the outside air in the winter
and cooling it in the summer, a variety
of technical heat recovery systems are in
use. A distinction is made between the following
methods:
Closed systems (heat pipe)
Cycle compound countercurrent systems
Plate-type heat exchangers
Heat wheels
Heat recuperators based on the heat
pump principle
HYGIENE SYSTEM
ETA SYSTEM
HP-WRG SYSTEM
HYDROPLUS SYSTEM
UV-UNIT
With the exception of the cycle compound
countercurrent system, all of the foregoing
are associated with potential risks of moisture
carryover or leakage air effects
which disqualify them for use in hygiene
applications.
HP heat recovery system with feedback circuit

Heat recovery based on a recirculation
system
Conventional systems operate with fairly
low efficiencies of around 40-50%. The
requisite additional heat or chill had to be
provided by supplementary heat exchangers
in the supply airflow. However, our
engineers have discovered a way of eliminating
this very disadvantage.
The HP* cycle compound heat
recovery system
This system comprises heat exchangers in
the exhaust air and fresh air. Between the
two heat exchangers, a heat transfer medium
is recirculated to carry the thermal
energy from one register to the other.
Using this design, our HOWATHERM HP
heat recovery system achieves efficiencies
of up to 80%.
*HP stands for high performance
How do we achieve this high
efficiency?
Factor 1: Design optimization
Our HP heat recovery system attains its
high efficiency of up to 80% by combining
multiple heat exchanger stages, each measuring
not more than 300 mm in depth in
conformance to VDI 3803 or VDI 6022. The
length of the assembled array varies bet-
Series arrangement of multiple heat exchanger
stages in countercurrent mode
ween 600 and 1200 mm, corresponding to
about 16 to 32 rows in the airflow direction.
To reduce the pressure loss, the in-flowing
air velocity must not exceed 2.5 m/s.
Factor 2: Accurate management
of the intermediate medium
Another important factor is the management
of the heat transfer medium circulating
between the heat exchangers. This
medium must get maximum
countercurrent
exposure in the heat
exchanger. We have the-
0,8
4
n = 5 stages
refore minimized crossflow
and eliminated all
0,7
3
co-current flow, since the
latter in particular gives
0,6
2
much lower transfer effi- 0,5
ciencies.
0,4
1
Our solution consists in
arranging the individual
heat exchanger stages in
series in a specific countercurrent
configuration
0,3
0 0,5 1,0 1,5 2,0
Stages in series
which must be strictly
Heat exchange rate as a function of the heat
adhered to. As a result of
this design, our system
attains a thermodynamic
flow capacity ratio at k x A / WW = const.
countercurrent rate of > 99%.
Factor 3: Control
Proper matching of the air mass flow and
water mass flow is of critical importance.
The maximum heat recovery rate is obtained
if the heat flow capacity of the two
media is the same. To this end, the flow of
the intermediate medium (e.g., brine) is
continuously controlled as a function of
the air mass flow. This is the only way to
ensure a maximum heat transfer even in
part-load operation.
WL = WW mL x cpL = mW x cpW At medium cp values
(cpL and cpW ), we thus obtain:
Construction
mL / mW = cpW / cpL mit cpW = 4.19 kJ/kg K und cpL = 1.01 kJ/kg K it follows that:
mL / mW = 4,19/1,01 = 4,15
3

4
Adjusting the speed
ETA SYSTEM
The complete
solution
Frequency converter ensures
contantly optimized conditions
Flow control via a throttle valve is an energy-inefficient
process which results in increased
pump wear.
Adjusting the speed of the circulator
pump through frequency control gives
optimum conditions.
The actual volumetric flow rate of the
transfer medium is measured by a magnetic
induction-type flow sensor with microprocessor
technology and an alphanumeric
display. An air flow measuring device
(VSM) on the air side supplies the target
signal (VSM for ETA systems). For details
refer to our ETA SYSTEM product information.
The complete solution - including
instrumentation and control components.
For our HP heat recovery system we supply
a compact supply module comprising all
hydraulic and instrumentation/control
components.
Designed for various air flows by accommodating
various circuit alternatives, this
module is optionally available with all
equipment components. The benefits are
obvious:
Supply module with complete hydraulic
system, even for expanded circuit configurations
such as indirect heat/cooling
supply via plate-type heat exchangers
Recovery of removed heat from dehumidification
and refrigerator wast heat is
integrated into the module
Free cooling is integrated into the
module, or available indirectly via a
plate-type heat exchanger
Field equipment for air and brine side
High operating reliability.
Our delivery comprises a switchgear cabinet
with DDC substation plus software tailored
to the specific application.
System adjustment and commissioning is
performed under instruction of our expert
fitters.
Energy optimized fan ETA System Switchgear cabinet with DDC substation
Enthalpy measurement
To determine the mean heat capacity of
the exhaust air under changing loads
(temperature and moisture), a temperature
sensor and an absolute moisture sensor
detect the mean heat content. These parameters
are used to determine the heat
flow capacity ratio.
Both variables are fed to the DDC substation
and processed accordingly.
The higher-order control system will then
supply only the system-specific target
values.

V SA
0....10 V
V ExtractA
FI
0....10 V
t SA
0....10 V
0....10 V
tExtractA X
Heat recovery-H
t FA
t 2 t 1
The anti-freezing function can be continuously
controlled via a three-way valve by
using the return flow temperature as the
controlled variable. Defrosting of a frozen
system (return flow tube surface temperature
< -3°C) can also be performed continuously
by adjusting the speed of the circulator
pump.
Performance testing
The performance data of our HP cycle
compound heat recovery system have been
confirmed by neutral experts. At the Technical
Academy of Central Switzerland,
Lucerne University of
Engineering, extensive measurements
were carried out on an
EN 45001-accredited test rig. Both thermal
performance data, e.g., transfer rates, and
pressure losses on the air and medium
side were determined according to EN 308.
Our calculated heat recovery rates of up to
89 % were demonstrated in practice.
M
Heat recovery-C
Schematic of the field equipment for heat recovery
improvement with PLC substation
SWISS
T E S T I N G
Pressure loss
350
300
250
200
150
100
50
50
4 6 8 10 12 14 16 18 20 22 24
Tube rows
40
30
20
4 6 8 10 12 14 16 18 20 22 24
Tube rows
In addition, the transfer
rates and pressure losses
of the heat exchanger
units were neutrally and
independently tested on RWTÜV
test rigs.
The performance data of our HP heat
recovery system have also been attested in
accordance
with the
European Standard
EN 308 as part of the
EUROVENT certification
system for AHU systems
(ID-No. AHU-98-05-001).
2,5 m/s
2,0 m/s
1,5 m/s
Transfer rates
90 1,5 m/s
2,0 m/s
80
2,5 m/s
70
60
freiwillig
GEPRÜFT
Betriebscharakteristik-Übertragungsgrad-Druckverluste
Transfer rates and
pressure losses/
tube rows
5

7
Secondary functions
HP heat recovery
system
Patents
Secondary functions
of the HP heat recovery
system
Apart from the primary heat
recovery function, a number
of secondary functions can
be implemented with this
technology. The interposition
of a heat transfer medium
makes it possible to supply
additional heating or cooling
of the heat transfer medium
without any additional heat
exchangers on the air side,
using water/water heat exchangers
only.
A direct supply of additional
media (e.g., cold water) via a
three-way valve is likewise
feasible.
For these functions (heating,
cooling), a HP system with a
heat recovery rate of at least
70% is required (VDI 2071).
Supply air
indirect heating
PHW
PCW
indirect cooling
Extract air
Outlet
PCW
direct cooling
M
M
Heat recovery-C
Venting devices
Drain points
Heat recovery-H
Example of a HP countercurrent heat recovery system
M
Entry
Downflow countercurrent tubing with automatic draining
and venting. Outlet / Venting devices / Drain points
Heat exchanger Patent Specification
P 195 14 167 German Patent 1997
P 198 08 753 German Patent 1999
Downflow countercurrent tubing with automatic
draining and venting
Outlet / Venting devices / Drain points

Supply air
Extract air
M
Power adjustment
Heating Dehumidification
Dehumidification cooling recovery
Extract air
Heating
indirect supply
Supply air
M
Hybrid indirect
adiabatic cooling
FI
M
M
M
Hybrid
condenser recooling
Refrigerating machine
wast heat
M
Changeover valve
Refrigerating
Cooling
Schematic of a typical embodiment: Summer operation
FI
M
M
M
Power adjustment
Exhaust air
indirect supply
M
Schematic of a typical embodiment: Winter operation
Fresh air
Exhaust air
Changeover valve
Refrigerating
Fresh air
Expanded functional
schematic showing
secondary functions
of the HP heat
recovery system
Schematic of a typical
embodiment:
Summer operation
Cold recovery
Indirect adiabatic evaporation
cooling
Refrigerating machine
wast heat
Indirect cooling
Dehumidification circuit
Dehumidification cold
recovery through integral
after-heating
Winter operation
Heat recovery
Indirect heating
5

8
Design
characteristics
Adiabatic cooling
In order to achieve the specified performance
for the HP heat recovery system
we have defined a number of minimum
design characteristics.
In the airflow direction the HP heat exchanger
consists of about eight rows in
the depth direction per register to make
the system as easy to clean as possible.
This design conforms fully to VDI 6022 and
VDI 3803 conditions. Registers with installation
depths exceeding 300 mm (staggered
arrangement) must be split in the
depth direction.
The individual registers are thus accessible
from each side and can be easily pulled
out for convenient cleaning to meet applicable
hygiene requirements.
During the summer months, adiabatic cooling
with the HP heat recovery systems has
been found to give good results. The adiabatic
cooling process is based on the use of
an integral humidifier in the exhaust air-
For enhanced corrosion protection our fins
are plastic-coated or made entirely of copper.
Aluminium fins are used for standard
operating conditions. We thus provide
ideal hygiene conditions due to optimum
cleaning characteristics.
The condensate need not pass the entire
heat exchanger but will collect in the condensate
tray after the individual registers.
Depending on the application, we either
use a staggered tube arrangement for
optimum performance characteristics or an
aligned tube system which minimizes pressure
losses at a slight penalty in terms of
transfer efficiency while being even less
susceptible to fouling.
The energy gained from the heat recovery
process is used for cooling in both winter
and summer operation, yielding further
energy savings.
Heat exchangers are optimized for thorough cleaning with water
flow which humidifies the extract air adiabatically
in several stages to cool it.
HYDROPLUS SYSTEM

Principle and operation
In our HYDROPLUS system, the heat exchanger
that is a necessary part of any airhandling
unit is simultaneously used as a
contact body. It is sprayed with water via
an array of nozzles in the extracted airflow
on the air inlet side. Air from the
system passing over the contact body is
adiabatically humidified in this process.
Design details
A contact body is assembled from numerous
aluminium fins arranged in parallel at
2,5 mm centers. The fins carry a durable
coating which increases its surface area
substantially while giving it lasting hydrophilic
properties, thus facilitating wetting.
At the same time, the coating protects the
contact body from corrosion.
Air humidification - how is it
achieved?
The spray is applied evenly to the entire
surface area of the contact body. The atomizing
nozzles create a very fine droplet
range. A film of water forms on the fins
and is exposed to laminar airflow. An
exchange of substances takes place between
the water on the fins and the air
passing over it.
What are the benefits?
The need for an additional humidifier
body, with attendant pressure loss, is eliminated.
We thus reduce the installation
length of the entire unit, saving on investment
cost.
The combination of both systems provides
further energy and cost savings.
Here, too, the component is used as a heat
exchanger and humidifier at the same
time.
The HP heat recovery / HYDROPLUS system
is divided into several stages. Each stage
comprises an adiabatic evaporation humidifier
providing adiabatic humidification
and hence, cooling, before the air enters
the next stage. If we compare this multistage
system to a single-stage arrangement,
we find that the separation of the
Hydroplus System - in combination with the HP heat recovery system
HOWATHERM
Contact-
humidifier
HYDROPLUS system
A contact humidifier
for adiabatic air
humidification
HYDROPLUS
SYSTEM
9

10
Performance gain
Advantages of the
combination system
HYDROPLUS in com-
bination with the HP
heat recovery
system
Design data
overall system into multiple stages provides
a performance gain of about 20%.
ϕ=1
Successive cooling steps increase the gain
of useful cold energy without causing a
proportional increase in investment cost.
Another important advantage lies in the
fact that the adiabatic humidification is
achieved via the evaporation humidifiers
integrated into the heat exchanger. No
additional pressure loss is incurred, as it
x
would be with separate humidifier bodies
which would in turn increase the energy
consumption.
All in all, we eliminate the need for a
separate humidifier body and reduce the
pressure loss and installation length of the
entire unit, all of which translates into
investment cost savings.
By combining an adiabatic humidification
of the extract air with the heat recovery
function in a single component, the following
additional benefits are obtained:
Reduced installation length
More energy savings through reduced
pressure loss
Lower investment costs
Retention of the fundamental advantages
of a contact humidifier, specifically
with regard to hygiene
22,0°C 23,9°C 27,0°C 32,0°C
40,0 %
11,8 g/kg 11,9 g/kg 11,9 g/kg 11,9 g/kg
63,1 l/h 45,7 l/h 45,4 l/h
24,0 Pa 24,0 Pa 24,0 Pa
60,0 %
25,0°C 21,6°C 23,3°C
26,0°C
19,7°C 21,1°C 21,0°C
11,9 g/kg 14,0 g/kg 14,7 g/kg 15,6 g/kg
Air flow . . . . . . . . . . . . . . . . . .10.000 m 3 /h
Cooling capacity . . . . . . . . . . . . . .33,1 kW
Heat recovery efficiency . . . . . . . . .71,4 %
Effective cooling efficiency . . . . . . . . .81,5 %
Humidification efficiency . . . . . . . . . . .94,2 %
Total operating water volume . .154,2 l/h at 2,5 bar
Stage dx (g/kg) mw (l/h) bw (l/h) bw/mw Sz (s) Pz (s)
1 2,1 25,2 63,1 2,5 7,0 53,0
2 0,6 7,3 45,7 6,3 5,0 55,0
3 0,9 10,9 45,4 4,2 5,0 55,0
Legend: mw . . .Evaporation volume bw . . . .Operating water volume
Sz . . . . Spray time Pz . . . . .Pause

Hygiene
The water quality should conform to VDI
Guidelines 3803.
Operation and control
HYDROPLUS SYSTEM
Advantages
The HYDROPLUS system as a contact humidifier
moves very small water volumes
with a low energy input. Water for humidification
is supplied via the normal utility
lines, without any pumps or rotary components.
The necessary nozzle inlet pressure
is about 2.5 bar when the system is in service;
this is adjusted via a pressure reducing
valve. Solenoid valves open and close
the nozzle groups to be activated/deactivated
in accordance with the required cooling
capacity.
Pre-investment analysis
The use of a heat recovery system is not
necessarily associated with a shorter payback
period.
Only a dynamic pre-investment analysis
based on VDI 2071 or SWKl Guideline 89-1,
which we will be glad to prepare for you
as a service, can ultimately provide a reliable
decision-making aid in selecting the optimum
heat recovery system for your project.
h
HYDROPLUS SYSTEM
I
II
III
x
h, x-diagram
ϕ=1 Stage I
Solenoid valve control
Stage III
Stage II
Pressure
Function Solenoid valve control
Our HP cycle compound heat recovery
system is the forward-looking alternative
to conventional low-efficiency heat recovery
solutions.
Adiabatic cooling in particular can provide
a range of interesting options to minimize
or eliminate mechanical refrigerating requirements.
It can thus provide a valuable
tool for saving energy and reducing environmental
loads.
Operation and
control
HYDROPLUS
SYSTEM
Pre-investment
analysis
11

For further information contact our inhouse
or agencies, or visit us on the
Internet.
HOWATHERM Klimatechnik GmbH
Innovative Ventilation and Air Handling
Technology
Degussagelände 11-15
55767 Brücken / Germany
Postal address:
Postfach 1461
55762 Birkenfeld / Germany
Phone: (+49) (0)6782-99 99- 0
Telefax: (+49) (0)6782-99 99-10
0700HOWATHERM
E-mail: info@howatherm.de
www.howatherm.de
We enjoy working with you.
SchillerKrenz-Gestaltung
©HOWATHERM KLIMATECHNIK GMBH
P006-07/03