Danfoss VXe Solo District Heating Substation: Installation and User Manual

Product Overview

The VXe Solo is an indirect, fully insulated district heating substation designed for connection to district heating networks. It provides heating and domestic hot water (DHW) services. The substation is characterized by its high insulation for very low heat losses.

Available models include:

VXe Solo H
VXe Solo HWP
VXe Solo HWS
VXe Solo H OP

2. Installation Instructions, Safety and Handling

General Safety: Read instructions carefully before installation and commissioning. Failure to comply may result in loss or damage. Installation, commissioning, and maintenance must be performed by qualified and authorized personnel in compliance with local safety regulations. Exceeding recommended operating parameters increases risk.

Energy Source: Primarily designed for district heating; alternative sources are acceptable if operating conditions are equivalent.

Application: Designed for water as heating medium. Install in a frost-free room with temperature not exceeding 50°C and relative humidity not higher than 80%. Ensure the substation is accessible and not covered or bricked in.

Materials and Corrosion: Pipes are made of AISI 304 (heating) and AISI 316 (domestic water) stainless steel, and dezincification-resistant brass. Heat exchangers are stainless steel, copper- or steel-soldered. Water quality (pH, chlorides, gases, temperature) significantly impacts scaling and corrosion. Refer to Section 18 for detailed guidelines on water quality.

Safety Valve: Installation must comply with local regulations.

Noise Level: 55 dB.

Storage: Store in a dry, heated (frost-free) room (max 80% humidity, 5-70°C). Do not stack higher than specified. Use packaging handles for lifting; use pallets for long distances. Do not lift by pipes to avoid leaks.

Connections: All energy sources, including electrical, must be disconnectable. Connect to an electrical equalizer.

Warnings: Hot surfaces can cause burns. High pressure and temperature (up to 120°C, 16 bar) in the district heating network pose scalding risks.

Emergencies: In case of fire, leaks, or hazards, shut off energy sources and call for assistance. If DHW is discolored or malodorous, shut off ball valves, notify users, and call for professional assistance.

Transport Damage: Check for damage upon reception before installation. Handle with care.

Tightening Connections: ALL pipe connections MUST be retightened before filling the system and again after the system is filled and operating. Do not overtighten (see page 15).

Handling: Wear suitable safety footwear.

Warranty: Interventions/rework on components results in loss of warranty.

REACH Compliance: Product contains brass parts with lead (CAS 7439-92-1) in concentration above 1% (w/w).

Equipotential Bonding: Important for protection against electric shock and reducing corrosion. Should comply with IEC 60364-4-41 and IEC 60364-5-54. The binding point is marked with a grounding symbol on the mounting plate.

Disposal: Dispose of packaging and product components according to local regulations. Do not dispose of with household waste.

3. Getting Started - Quick Guide for Easy Start-up

Mounting: Connect the substation to household piping as per labeling or manual instructions. Mount on a solid wall using sturdy bolts (max. 8 mm), screws, or expansion bolts.

Connections: Tighten all pipe connections, as they may have loosened during transport. Mount the district heating meter. Establish a drain connection for safety valves if applicable.

Filling & Testing: Fill the heat exchanger/system with water (see page 16). Open HE supply and return ball valves and heat the system. Check thoroughly for leaks and pressure test the entire system.

Electrical: Connect pump and automatic components to electricity, but do not switch on power yet. Vent the radiator circuit/heating side.

Operation: Switch on the pump and automatic components. Adjust the substation as per instructions and complete the Commissioning Certificate (page 34).

Notes: Heating and cooling may cause leaks; retighten connections after commissioning. Never lift the station by its front insulation cover.

Connections Diagram:

DH supply
DH return
HE return
HE supply
Cylinder supply
Cylinder return

4. Main Components / Connections

The VXe Solo substations are equipped with various components depending on the model. Key components include:

Plate heat exchanger (HE) with insulation
Strainer
Ball valves
Circulation pump (HE)
Safety valve (HE)
Thermometer
Pocket for pressure gauge / Manometer
Expansion vessel
Controller (Danfoss ECL 310)
Actuator (Danfoss AMV)
Flow controller (AVQM, VS2)
Optional: Safety thermostat (Jumo AT)

VXe Solo H / VXe Solo H OP: Typically use AVQM flow controller with integrated control valve and AMV actuator.

VXe Solo HWP: Features a differential pressure controller (AVPB-F) and VS2 valve with AMV actuator.

VXe Solo HWS: Includes circulation pump for cylinder circuit and controls via ECL, AVQM, and AMV.

Accessories: KFE tap for filling/draining, Thermostatic valve RAVK/VMA for DHW.

5. Diagram & Dimensional Sketch, Example

Detailed diagrams and dimensional sketches are provided for each model (VXe Solo H, HWP, HWS, H OP), illustrating component layout, connections, and overall dimensions. These diagrams include numbered components corresponding to the lists in Section 4.

Connections are typically labeled as:

1. District heating (DH) supply
2. District heating (DH) return
3. Heating (HE) return
4. Heating (HE) supply
5. Cylinder supply (for HWP/HWS)
6. Cylinder return (for HWP/HWS)

Technical drawing information such as general tolerance accuracy (ISO 2768 - mK), scale, size, material, and weight are also provided.

6. General, Mounting of Heat Meter and Safety Valves

General: Installation and maintenance by qualified personnel. Ensure free access. Mount substation on a solid wall using the mounting plate/rear section and 4 bolts (max. 8 mm).

Preparation: Rinse household piping and clean dirt strainers before commissioning.

Insulated Systems: The front insulation panel can be removed tool-free by pulling the air duct.

Test and Connections: Retighten all pipe connections before filling. After filling, retighten again before pressure testing. After heating, check and retighten if necessary. Note EPDM rubber gaskets; DO NOT OVERTIGHTEN to prevent leaks. Leaks due to overtightening or failure to retighten are not covered by warranty.

Meter Display: Located on the console with the ECL regulator for easy reading.

Heat Meter Fitting: Substation is equipped with fitting pieces (3/4" x 110 mm) for heat meters on the DH return line. Follow specific steps for fitting heat meters, including closing ball valves, removing fitting pieces, installing meter and sensors, and retightening connections.

Safety Valves: Lead blow-off pipes to a drain in compliance with legislation. The insulation cover is prepared for this.

7. Filling the System with Water

Pre-filling Checks: Ensure pipes are connected correctly, expansion vessel is connected, heat meter is mounted, shut-off valves are closed, connections are tightened, and recirculation (if any) is established.

Filling Procedure:

Ensure the pump is switched off.
Open ball valves for HE supply and return flow.
Fill the system with water while venting.
Fill until the manometer shows a working pressure (approx. 1.2 - 1.5 bar, corresponding to system height + 5 m).
Open remaining ball valves and heat the system.
Vent the system (radiators and air vents).
Switch on the pump.

Note: No internal filling valve is present; use a refill hose. Filling is typically done via a cold water supply connection in the household installation. A KFE tap accessory is available.

8. Electrical Connection

General: Electrical connection must be performed by a qualified electrician according to all applicable rules and regulations. Connect to a 230 V AC power supply. Ensure the station can be disconnected via an external main switch for maintenance or emergencies. Establish potential equalization.

Controller: VXe Solo models are delivered with Danfoss ECL Comfort 310 controllers, with actuators and sensors pre-mounted. The station is factory wired and tested.

Outdoor Temperature Sensor (ESMT): Mount on the coldest side of the property, away from direct sunshine, heat sources, windows, doors, air vents, balconies, and eaves. Mounting height is approx. 2.5 m. Connect to the ECL controller (common ground terminal and terminal 29). Access to the ECL base part is via a lock mechanism.

Specifications:

ECL Comfort 310: 230 V AC, 50 Hz, 5 VA consumption, 4(2) A relay output, 0.2 A triac output.
Actuator AMV 150: 230 V AC, 50 Hz, 2/8 VA consumption.
Pump UPM3 AUTO: 230 V AC, 50 Hz, IP44, Max. 52 Watt.

9. Adjustment and Commissioning

General: Some models may have slight visual differences, but control functions are similar.

Commissioning: Follow the instruction manual. Fill the unit with water as per page 16. Maintain operating pressure between 1 and 1.5 bar (safety valve opens at 2.5 bar). If pressure drops rapidly, check for leaks and expansion vessel pressure (factory set at 0.5 bar).

Differential Pressure Controller: Reduces and stabilizes district heating network pressure. Models like VXe Solo HWP use AVPB-F, preset from the factory. Other models use AVQM with an integrated control valve.

10. Heating Circuit, Danfoss ECL 310 Automatics

Control: Weather-compensated control of the heating circuit is managed by the Danfoss ECL 310 controller. It calculates supply temperature based on outdoor temperature. The controller uses an ECL Application Key for settings and language.

Factory Settings: Typically include English language, Comfort operating mode (Sun symbol), and application type (A230/A337/A237). Motor speed and protection are pre-set and tested.

Start-up: Ensure the outdoor sensor is correctly installed and connected. Power on the controller, select MENU, navigate to 'Common controller settings', set time and date. The controller is then ready for use.

Setting Heat Curve & Max Temperature: Navigate to MENU > Heating circuit > Settings > Flow temperature. Adjust 'Heat curve' and 'Temp. max.' according to system type (e.g., one-string, two-string, floor heating). Typical ranges are provided for heat curve (1.0-1.75) and max temperature (35-90°C).

11. Control of Heating Circuit

VXe Solo H, HWS, H OP: Equipped with a self-acting flow controller (Danfoss AVQM) and an actuator (Danfoss AMV) on the primary return flow line. The AVQM controls max flow and has an excess pressure safety valve. The AMV actuator is electrically wired to the controller.

VXe Solo HWP: Uses a Danfoss AMV 150/13 actuator and a two-way motorized control valve (Danfoss VS 2) on the primary return flow line.

Actuator Operation: AMV actuators are factory tested and preset. Manual override is possible. AMV 13 valve behavior depends on safety function settings when power is off.

Safety Function: Jumo AT safety thermostat can be fitted for overheating protection, pre-wired to the ECL controller.

Manual Override: For AMV 150, turn the knob clockwise. For AMV 13, press and hold a button on the bottom side during manual operation.

12. Heating Circuit, Pump

Grundfos Pump UPM3 AUTO: Features 12 optional settings selectable via a push-button. Factory setting is Proportional Pressure 2.

User Interface: Displays operation status, alarm status, and allows settings adjustment. LEDs indicate power consumption and status.

Changing Settings: Press the button to view settings. To change, press and hold for over 2 seconds (less than 10), LEDs flash to show current setting. Press until desired setting is shown, then release. LEDs flash to confirm save. The pump can be locked/unlocked by pressing the button for over 10 seconds.

Pump Modes: Includes Proportional Pressure (e.g., Pressure 1, 2, 3), Constant Pressure (e.g., Constant Pressure 1, 2, 3), and Constant Curve (e.g., Constant Curve 1, 2, 3 MAX.).

Alarm Status: Indicated by the 1st LED turning red. Alarms include Function Blocked, Supply voltage low, and Electrical error.

13. Domestic Hot Water (DHW)

General: VXe Solo HWP has primary side cylinder connections; VXe Solo HWS has secondary side cylinder connections.

VXe Solo HWP: DHW cylinder control is optional. Can be equipped with a RAVK self-acting thermostat and VMA 2-way valve for temperature regulation.

VXe Solo HWS: Cylinder temperature is controlled by the Danfoss ECL controller, AVQM flow controller, AMV 150 actuator, and a cylinder sensor. The application key is pre-configured for the system type. Desired DHW temperature must be set during commissioning.

VXe Solo HWS (ECL 310/A237): Uses AVQM and AMV 13 actuator for cylinder temperature control.

DHW Circulation Pump: VXe Solo HWS models with secondary cylinder connections are fitted with a Grundfos UPM3 Auto pump, controlled by the cylinder sensor and ECL controller.

Summary Table:

Type	Primary Connection for Cylinder	Secondary Connection for Cylinder	Pump for cylinder circuit	Control
VXe Solo HWP (ECL310/337)	Yes	No	Not part of delivery	Control not part of delivery
VXe Solo HWS (ECL310/A337)	No	Yes	Grundfos UPM3 Auto	Danfoss ECL 310, Application A337 (AVQM / AMV 150)

Diagrams: Illustrate VXe Solo HWP with primary connection and VXe Solo HWS with secondary connection for the cylinder.

14. Maintenance

General: Maintenance work must be performed only by qualified and authorized personnel.

Inspection: Regularly check the water heater. Maintain according to instructions. During service, clean dirt strainers (including controller filter), tighten pipe connections, and function-test safety valves.

Plate Heat Exchanger Cleaning: Rinse with clean water at high speed in the reverse direction of normal flow. If insufficient, circulate approved cleaning agents (e.g., Kaloxi, Radiner Fl). Rinse thoroughly with clean water afterward.

Acidification: Not recommended for brazed plate heat exchangers. If necessary, use dilute acid solutions (5% formic, acetic, or phosphoric acid). Rinse thoroughly after use.

Post-Maintenance: Check all screwed connections, replace covers, clean the work area, connect to energy supply, check for leaks, vent the system, perform adjustments, and ensure all safety features function correctly.

Meter Reading: Caretaker/owner should perform visual checks and readings of the district heating meter regularly. Excessive consumption is not covered by warranty.

Cooling/Return Temperature: The difference between supply and return temperatures (typically 30-35°C) affects energy economy. Focus on return temperatures from the heating circuit and circulation water.

Warranty: Use of packaging other than original will void warranty.

14. Maintenance Schedule (Recommendations)

Interval	Maintenance Work	Comments
At least once per month*	Read the meter and check the system and all connections for leaks	Enter readings in control book; contact personnel for leaks.
At least once per year*	Check pipes and exchanger for corrosion/coatings.	Visual control. Replace exchanger if coatings are present.
	Check all connections for leaks.	Replace gaskets and retighten connections if leaks are found.
	Check safety valve functionality.	Test by turning the lever. Replace faulty components.
	Clean all dirt filters/strainers.	Replace any filters that are not intact.
	Check electrical cables and power disconnection capability.	Visual check. Ensure power can be disconnected.
	Check pipes and exchanger for corrosion.	Visual check.
	Check insulation cover integrity.	Ensure it encloses the substation tightly.
	Check temperature regulator settings.	Follow manual instructions.
	Check functions of all shut-off valves.	Ensure ball valves open and close correctly.

*) Enduser/caretaker. Note! Gaskets MUST be replaced after maintenance.

15. Troubleshooting - Heating (HE)

Fundamental Checks: Ensure correct connections, normal DH supply temperature and differential pressure, power supply to pump/automatics, clean dirt strainer, and no air in the system.

Problem	Possible Cause	Solution
Too little or no heat	Strainer clogged (DH or HE circuit)	Clean strainer(s).
	Filter in energy meter clogged	Clean filter (consult DH plant operator).
	Defective or improperly adjusted differential pressure controller	Check operation; clean valve seat if required.
	Defective sensor	Check operation; clean valve seat if required.
	Automatic controls wrongly set or defective; power failure	Check settings and power supply. Set motor to manual control temporarily.
	Pump out of operation	Check power to pump and rotation. Check for air in pump housing.
Uneven heat distribution	Pump set at too low speed	Set pump to higher speed.
	Air pockets in the system	Vent the installation thoroughly.
	Limiting of return temperature adjusted too low	Adjust according to instructions.
	Defective radiator valves	Check and replace.
	Incorrectly set balancing valves or no balancing valves	Adjust/install balancing valves.
	Pipe diameter too small or branch pipe too long	Check pipe dimensions.
	Defective controller or control valve	Set controls correctly; replace control valve.
DH supply temperature too high/low	Defective controller	Set controls correctly.
	Strainer clogged	Clean strainer.
Too high DH return temperature	Heat load too high; small heating surface/radiators	Increase heating surface; ensure even heat distribution across heating surface; keep supply temperature low.
	Poor utilization of heating surface; defective sensor	Ensure even distribution; check sensor.
	Single pipe loop system	System should be equipped with electronic controllers and return sensors.
	Pump pressure too high	Set pump lower.
	Air in system	Vent system.
	Defective or incorrectly set radiator valve(s)	Check/set/replace.
	Dirt in differential pressure controller	Check and clean.
	Defective motorized valve, sensor, or automatic controller	Check and replace.
Noise in system	Pump pressure too high	Adjust pump to a lower level.
	Noice from radiator valves	Check flow direction.
	Defective motorized valve, sensor, or electronic controller	Check and replace.

Disposal: Dismantle and sort components for recycling or disposal according to local regulations.

15. Troubleshooting - Domestic Hot Water (DHW)

Fundamental Checks: Ensure correct connections, normal DH supply temperature and differential pressure, power supply to pump/automatics, clean dirt strainer, and no air in the system.

Problem	Possible Cause	Solution
Too little or no DHW	Dirt strainer in DH supply line clogged	Clean the dirt strainer.
	Charging pump out of operation or set too low	Check pump operation and power; check for air in pump housing.
	Defective actuator or dirt in valve housing	Check actuator functions; clean valve seat if required.
	No power	Check power supply.
	Automatic controls wrongly set or defective	Check settings; set actuator to manual control temporarily.
	Calcified plate heat exchanger	Replace.
	Defective actuator or thermostat	Check according to manual; replace.
	Defective or clogged non-return valve	Replace or clean.
	Defective immersion sensor	Replace sensor.
	Inadequate cylinder capacity	Check manufacturer specifications.
Hot water available only at some taps	Cold and warm drinking water mix (e.g., defective thermostatic mixing valve)	Check and replace mixing valve.
DHW temperature too high	Non-return valve on circulation line defective	Replace non-return valve.
	Thermostatic valve RAVK/VMA set too high	Check and adjust.
Declining temperature during tapping	Calcified heat exchanger	Replace.
	Temperature difference between supply flow and DHW setpoint too low	Choose a lower DHW setpoint or increase supply water temperature.
	Calcified heating element	Clean DHW cylinder or replace heating element.
Temperature falls during tapping (lack of capacity)	Controller incorrectly adjusted or defective	Check controller settings.
	Immersion thermostat sensor incorrectly fitted	Place sensor correctly per manufacturer specifications.
	Calcified heating element	Descale heat exchanger or replace element.
Temperature too high	Defective actuator / dirt in valve housing	Check actuator functions; clean valve seat.
	Automatic controls wrongly set or defective	Check controller settings.
	Defective immersion sensor	Replace sensor.
	Calcified heating element	Clean DHW cylinder or replace element.
	Insufficient cylinder capacity	Check cylinder capacity.

16. EU Declaration of Conformity

The VXe Solo substations comply with relevant EU directives. A declaration of conformity is provided.

17. Commissioning Certificate

Pre-Commissioning: The substation links district heating supply to household piping. All pipes must be checked and rinsed. After filling with water, retighten all connections before pressure testing. Clean dirt strainers and adjust the substation per instructions.

Compliance: Adhere to all technical regulations and applicable legislation. Installation and commissioning must be performed by trained, authorized personnel.

Factory Checks: The substation is factory leak-checked. However, vibrations during transport and handling may cause leaks, so re-checking and retightening connections before commissioning is crucial. Avoid overtightening EPDM gaskets.

Installer Information: The certificate requires completion by the installer, including date, company name, and confirmation of retightening, adjustment, and commissioning.

18. Guidelines for Water Quality in Danfoss Brazed Heat Exchangers

Maintaining proper water quality is essential for the longevity and performance of heat exchangers. The following table outlines recommended parameters and their impact on corrosion resistance for different materials (AISI 316L, Cu, CuNi, StS).

Parameter	Unit	Value or concentration			Plate AISI 316L W.Nr. 1.4404	Brazing material
		< 6.0	6.0 – 7.5	7.5 – 10.5	>10.5	Cu	CuNi	StS
pH		o	+	+	+	+	+	+
Conductivity	µS/cm	o	+	+	+	+	+	+
Free Chlorine	mg/l	o/-	+	+	+	+	+	+
Ammonia (NH3, NH4+)	mg/l	+	+	o	o/-	+	+	+
Alkalinity (HCO3-)	mg/l	+	+	+	+	+	+	+
Sulphate (SO42-)	mg/l	+	+	+	+	+	+	+
HCO3- / SO42-		+	+	+	+	+	+	+
Nitrate (NO3)	mg/l	+	+	+	+	+	+	+
Manganese (Mn)	mg/l	+	+	+	+	+	+	+
Iron (Fe)	mg/l	+	+	+	+	+	+	+
Hardness ratio [Ca2+, Mg2+]/[HCO3-]		+	+	+	+	+	+	+

Key: + Good corrosion resistance, o **Corrosion could happen when more parameters are evaluated with o, o/- Risk of corrosion - Use is not recommended. * Hardness ratio limits defined per experience and internal tests. ** In case of three or more parameters evaluated with 'o', consultancy is needed.

Recommended Chloride Concentration to Avoid Stress Corrosion Cracking (SCC):

At T ≤ 20°C: max 1000 mg/l
At T ≤ 50°C: max 400 mg/l
At T ≤ 80°C: max 200 mg/l
At T ≤ 100°C: max 100 mg/l

For more information, visit: Danfoss Water Quality Guidelines.

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Danfoss VXe Solo District Heating Substation