Shunt groups and protection against freeze damage

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1 Shunt groups and protection against freeze damage Application in air handling units EF RC1 ROOM * * GT2 GT2 GT2 ST1 GT3 SF SECONDARY GT8 CIRCUIT, HEAT SECONDARY CIRCUIT, COOLING GT1 HRC AIR HANDLING UNIT (AHU) CP2 SF EF CP2 HRC GT1 GT2 GT3 GT8 Supply air fan Extract air fan Circulation pump, heat Circulation pump, cooling Rotary heat exchanger Supply air sensor Extract air sensor/room sensor (*alternative location) Outdoor air sensor Freezing protection monitor SHUNT GROUP, HEAT, WITH TWO-WAY REGULATING VALVE SV2 SHUNT GROUP, COOLING, WITH TWO-WAY REGULATING VALVE Regulating valve (shunt) and actuator, heat SV2 Regulating valve (shunt) and actuator, cooling ST1 Outdoor air damper actuator RC1 Microprocessor unit (controller) PRIMARY CIRCUIT, DISTRICT HEATING SYSTEM PRIMARY CIRCUIT, DISTRICT COOLING SYSTEM

Shunt groups and freeze damage protection for air handling units Shunt groups A shunt group is an assembled unit consisting of a regulating valve, circulation pump, initial adjustment valves,

2 Shunt groups and freeze damage protection for air handling units Shunt groups A shunt group is an assembled unit consisting of a regulating valve, circulation pump, initial adjustment valves, shut-off valves, etc. The purpose of the shunt group is to serve as a link between primary and secondary systems in waterborne heating and cooling systems, e.g. between a boiler (primary circuit) and a heating coil inside an air handling unit (secondary circuit). The pipework package is required for regulating the capacity to meet the heating or cooling load since the secondary system most often operates with other temperatures and flows than the primary system. The capacity is regulated as follows: The shunt group mixes the media (primary/secondary) in a controlled manner to achieve the correct temperature in the secondary system. Typical prefabricated shunt group (Siemens) Basic circuit diagram showing the makeup of a prefabricated shunt group (Siemens) A shunt group usually consists of the following components: Regulating valve Regulates the flow in the shunt group s primary and secondary circuit. The regulating valve is operated by a valve actuator wired to a control unit. The regulating valve is used for obtaining the correct water temperature in a heating or cooling system. The regulating valve, also called shunt valve, mixes inlet water from the primary circuit with water from the return pipe (secondary circuit). The regulating valve can be of two-way or three-way design depending on the nature of the pipe system to which it will be connected. Circulation pump Keeps the liquid circulating in the circuit on the secondary side. Manual commissioning valve For adjusting (balancing) the flow and pressure drop to achieve an optimum shunt group duty point. Manual shut-off valve Enables you to dismantle the shunt group without having to empty the entire system. Bypass with non-return valve Enables circulation of liquid in the shunt group s secondary circuit, as indicated by the flow arrow, even if the regulating valve is closed against the secondary circuit. Prevents the medium from flowing in the wrong direction in the event of a power failure to the secondary circuit pump. Thermometers Provide an overview of the operating conditions and to show how the system is operating. 2

3 Examples of shunt groups Two-way regulating valve Pipework package (code STD-05) Primary Secondary Primary Pipework package Secondary Översikt H2O H2O H2O Top Shunt group with two-way regulating valve fitted in the return pipe from a heating or cooling coil. Variable flow in the primary circuit Constant flow in the secondary circuit Suitable for use in e.g. district heating/district cooling systems in which low or high return temperatures are desirable. Bleeder valve, if required, enables the circulation of water to the secondary circuit. Used e.g. to quickly supply heat/cooling energy to the coil (in long supply flow pipes) or for outdoor installation. Three-way regulating valve Pipework package with three-way regulating valve fitted in the supply pipe to the heating coil. The flow can be commissioned with the rated KVS value of the regulating valve. Variable flow in the primary circuit Constant flow in the secondary circuit Suitable for use in e.g. district heating systems in which low return temperatures are desirable and in systems with low primary pressure. Adjustment valve, if required. Commissioning is normally carried out with the rated Kvs value in the pipework package. (IV Produkt regulating valve (code STD-05) has variable Kvs). Compact Flex Primary Secondary H2O * The Kvs value expresses the amount of 20-degree water flow (m³/h) allowed to pass through a fully open regulating valve at 100 kpa motive pressure. Example: A regulating valve with a Kvs value of 16 allows 16 m³/h (4.44 l/s) to pass through at 100 kpa (1 bar) motive pressure. Styr H2O Shunt group with three-way regulating valve fitted in the return pipe from a heating or cooling coil. Constant flow in both the primary and secondary circuits. Suitable for use in systems with their own source of energy, e.g. boiler systems, in which constant flow in the primary circuit and a slight drop in temperature are desirable. The pump in the shunt group forces a constant flow of water through the coil and the three-way valve mixes a portion of the primary water with a portion of the return water from the coil, to provide the correct ultimate capacity. Filteröversikt Kodnycklar 3

4 Basic circuit diagrams, shunt groups in ventilation installations District heating and district cooling EF RC1 ROOM * * GT2 GT2 GT2 ST1 GT3 SF GT8 SECONDARY CIRCUIT, HEAT SECONDARY CIRCUIT, COOLING GT1 HRC AIR HANDLING UNIT (AHU) CP2 SF EF CP2 HRC GT1 GT2 GT3 GT8 Supply air fan Extract air fan Circulation pump, heat Circulation pump, cooling Rotary heat exchanger Supply air sensor Extract air sensor/room sensor (*alternative location) Outdoor air sensor Freezing protection monitor SHUNT GROUP, HEAT, WITH TWO-WAY REGULATING VALVE SV2 SHUNT GROUP, COOLING, WITH TWO-WAY REGULATING VALVE SV2 ST1 RC1 Regulating valve (shunt) and actuator, heat Regulating valve (shunt) and actuator, cooling Outdoor air damper actuator Microprocessor unit (controller) PRIMARY CIRCUIT, DISTRICT HEATING SYSTEM PRIMARY CIRCUIT, DISTRICT COOLING SYSTEM Example: Two-way shunt groups in a ventilation installation with district heating and district cooling The illustration shows pipework packages with two-way regulating valves fitted in the return pipes from heating and cooling coils. The pipework connections that are suitable for district heating and district cooling involve the following: The primary circuit operates with variable flow The secondary circuit operates with constant flow A low return temperature (substantial Δt) is obtained in the heating case A high return temperature (substantial Δt) is obtained in the cooling case A bleeder valve, if required, enables the circulation of water forward to the secondary circuit to quickly supply heat/cooling energy to the coil (e.g. in the case of long supply flow pipes). Since a district heating plant s distribution pipes often are long, the greatest portion of the costs for water produced for district heating is for distribution. It is therefore important to extract necessary heating capacity out of as little water flow as possible, which means that in the case of district heating a substantial decrease in water temperature is required. 4

5 Private heat source and private cooling plant EF RC1 ROOM * * GT2 GT2 GT2 Översikt ST1 GT3 SF GT8 SECONDARY CIRCUIT, HEAT SECONDARY CIRCUIT, COOLING GT1 Top HRC AIR HANDLING UNIT (AHU) Compact CP2 SF EF CP2 HRC GT1 GT2 GT3 GT8 Supply air fan Extract air fan Circulation pump, heat Circulation pump, cooling Rotary heat exchanger Supply air sensor Extract air sensor/room sensor (*alternative location) Outdoor air sensor Freeze protection monitor SHUNT GROUP, HEAT, WITH THREE-WAY REGULATING VALVE SV2 SHUNT GROUP, COOLING, WITH THREE-WAY REGULATING VALVE Flex SV2 ST1 RC1 Regulating valve (shunt) and actuator, heat Regulating valve (shunt) and actuator, cooling Outdoor air damper actuator Microprocessor unit (controller) PRIMARY CIRCUIT, HEAT PRIMARY CIRCUIT, COOLING Styr Example: 3-way shunt groups in a ventilation installation with boiler and private cooling plant The illustration shows shunt groups with three-way regulating valves fitted in the return pipes from heating and cooling coils. The pipework connections that are suitable for e.g. a boiler and your own cooling plant involve the following: Both the primary and secondary circuits operate with constant flows The regulating valves mix the supply flow and return water (mixing valve) Relatively little drop in temperature (little Δt) is obtained. If the water is heated by means of a boiler/centralized boiler, the requirement for temperature reduction in the water is normally not as much as for district heating. Too low return temperature may cause condensation to form inside the boiler. Filteröversikt Kodnycklar 5

6 Shunt data from IV Produkt Designer The IV Produkt Designer product selection program computes the shunt data for both two-way and three-way regulating valves according to the examples below. The shunt data consists of Liquid temp in, Liquid temp out and Liquid flow. Envistar Flex Project AHU Size Technical data Project1 AHU /1.80 m³/s AIR HEATER WATER Input Air temperature in 13.3 C Requested air temp out 20.0 C Liquid temp in 82.0 C Liquid temp out requested 71.0 C Output Air temperature out 20.0 C Air speed 1.9 m/s Liquid flow 0.10 l/s Pressure drop liquid 0.3 kpa Power variant 00 Heating power 14.5 kw Fin pitch 6.0 mm Tube connection 25 Alt. 1 Primary side with 2-wayvalve Liquid temp in 82.0 C Liquid temp out 45.9 C Liquid flow 0.10 l/s Alt. 2 Primary side with 3-wayvalve Liquid temp in 82.0 C Liquid temp out 71.0 C Liquid flow 0.32 l/s Example: Technical data from IV Produkt Designer Temperatures and flows at design drop in temperature according to data above: SEK. 0,10 l/s 0,10 l/s SEK. 0,10 l/s 0,10 l/s 45,9 C 82,0 C 45,9 C 82,0 C 0,22 l/s 45,9 C 82,0 C 71,0 C 82,0 C PRIM. 0,10 l/s 0,10 l/s PRIM. 0,32 l/s 0,32 l/s Alt. 1 Two-way regulating valve Alt. 2 Three-way regulating valve 6

7 Sizing of coils The water temperature specified in technical data (examples on the previous pages) is obtained only when the design Air temperature, out has been reached. The liquid flow through a coil should be kept constant to achieve the best heat transfer characteristics. The Capacity is regulated by changes in water temperature which take place preferably in a pipework package. If the flow of liquid in a coil is too low, the coil will never operate optimally and there is high risk of freeze damage, laminar flow* and difficulty in regulating the temperature. Things to consider... iquid Liquid pressure drop. Acceptable liquid pressure drops for coils vary depending on how they are used. As approx. values for sizing, we recommend the following (which refer to coils installed in air handling units): - Heating coil, clean water < 15 kpa - Cooling coil, clean water < 30 kpa Cooling coil for air velocities more than ~2.8 m³/s we recommend the use of droplet separators (applies to standard aluminium fins. If the fins have been painted with Corropaint, the corresponding limit value is ~1.5 m³/s. Översikt Top * There are two types of flows: laminar and turbulent. At low airflow velocities the flow can occur in parallel stratifications and this is called laminar. Laminar flow is difficult to regulate/stabilize and has proportionately poor heating and cooling transfer. Flows normally consist of vortex movements of varying size and frequency. Flows of this type are called turbulent. When the flow is turbulent, friction and heat/cooling energy transfer is considerable greater than in the case of laminar flow. Compact Flex Kodnycklar Filteröversikt Styr 7

8 Freeze protection function for heating coils IN OUT General The purpose of freeze protection is to prevent ice from forming in the rows of tubes in the heating coil. If any ice should form, this could cause the heating coil to freeze and burst resulting in water damage. To prevent ice from forming on surfaces, the heating coil should be fitted with a freeze protection sensor/ freeze protection monitor wired to a microprocessor unit/controller. The microprocessor unit protects the heating coil by performing the following sequence: When the air handling unit is operating Opens the regulating valve if the water temperature drops below 12 C (preset value) Switches off the fans and closes the outdoor air damper if the water temperature drops below 5 C (preset value) When the air handling unit has stopped Starts the function for keeping the coil warm by regulating the regulating valve to achieve the preset stay-warm temperature of 20 C (preset value) and in this way prevent frost from forming and making the air handling unit easy to start up. The location of the temperature sensor is very important because the sensor must be able to sense if the temperature drops too low. The sensor must therefore always be located on the coldest point of the heating coil by the return/outlet pipe. Air OUT Air IN Counter-flow coupling versus parallel-flow coupling In the following information, we refer to counter-flow coupling only, since it offers the best capacity and is most common. Clamp-on sensors Clamp-on temp. sensors are mounted to be in direct contact with the outlet pipe of the heating coil. Air Clamp-on temperature sensor OUT IN Clamp-on temp. sensor location: supply air, from left to right The temperature sensors are available in two versions: Clamp-on sensors Immersion sensors. Counter-flow or parallel-flow coupling? The tube rows of a heating coil can be connected/ coupled either for counter flow or parallel flow. Counter-flow coupling means that the warm supply flow water meets the airflow. The warmest section of the coil will be where the air leaves the coil. Counterflow coupling offers the highest heating capacity. IN OUT Clamp-on temperature sensor Air Parallel-flow coupling means that the warm supply flow water follows the direction of airflow. This results in poorer heating capacity. Clamp-on temp. sensor location: supply air, from right to left 8

9 Immersion temperature sensor Insert an immersion temp. sensor into the coil through the coil s built-in connection nipple. Depending on the direction of airflow through the coil (supply air flowing from left to right or vice versa) install the immersion sensor at the bottom or top to sense the cold spot. See the following illustrations. Flex Compact Top Översikt IN Air Styr OUT Immersion temp sensor Filteröversikt Immersion temp. sensor location, supply air, from left to right Kodnycklar Immersion temp. sensor location, supply air, from left to right 9

10 Immersion temp sensor OUT Air IN Immersion temp. sensor location, supply air from right to left Immersion temp. sensor location, supply air from right to left 10

ThermoGuard Coils protected from freezing with ThermoGuard have been developed as a result of the discovery that ice itself is not

The pressure of the water closed in by the ice is what eventually causes the bursting.

The pressure is led away to the pipe system or through a safety valve (SÄV).

ThermoGuard function Things to consider... Install the clamp-on and immersion temp. sensors according to the instructions.

11 ThermoGuard Coils protected from freezing with ThermoGuard have been developed as a result of the discovery that ice itself is not what causes the tube bends to burst. Freezing occurs first inside the tubes in the finned-tube package. The pressure of the water closed in by the ice is what eventually causes the bursting. The ThermoGuard function relieves the high water pressure inside the tube bends and prevents the bends from bursting. The pressure is led away to the pipe system or through a safety valve (SÄV). ThermoGuard offers increased safety against freeze damage. ThermoGuard coils are connected in the same way as other coils. ThermoGuard function Things to consider... Install the clamp-on and immersion temp. sensors according to the instructions. Insulate around the sensor where it is mounted to ensure that it will operate correctly. Översikt Top Compact Hot water return Pressure relief hole Safety valve Flex Hot water inlet Filteröversikt Kodnycklar Styr Safety valve on ThermoGuard heating coils protected against freezing 11

12 IV Produkt AB, Box 3103, Växjö, Sweden Phone: Fax:

ECONET PREMIUM FAQ TROUBLE-SHOOTING: GT 21 GT 20 GT 00 GF 10 GT 10. Start by checking all indata for the air handling unit.

ECONET PREMIUM FAQ TROUBLE-SHOOTING: GT 21 GT 20 GT 00 GF 10 GT 10. Start by checking all indata for the air handling unit. ECONET PREMIUM TROUBLE-SHOOTING: Start by checking all indata for the air handling unit. 2 Air temperatures/humidity Outdoor air temperature C Thermometer or AHU/Econet Supply air temperature C Thermometer