Constantly rising energy costs and strict legal requirements demand highly accurate billing of the thermal energy consumed in heating and cooling systems. Together with the volume flow sensor, precise temperature sensors, which are manufactured and approved according to DIN EN 1434, form the core of the measurement.
The calibratable temperature probes determine the temperature difference between the supply and return flow. Together with the measurement of the volume flow, the determined temperature difference provides the basis for calculating the heating bill. We offer you fully paired temperature probes for this demanding application in billing systems.
Testo Sensor GmbH not only manufactures temperature probes according to your customer-specific requirements, but also keeps track of all relevant standards and guidelines for proper approval for you. In this guide, we have compiled everything you need to know when selecting, purchasing, installing and operating your temperature probe for energy meters
What are temperature sensors for energy meters?
Temperature sensors for energy meters are high-precision measuring devices that have been specially developed for measuring temperature differences in heating and cooling systems. Together with the flow sensor, they form the core of every heat meter and enable the exact billing of the thermal energy consumed.
How does the measurement work?
The recording of thermal energy is based on a physical principle: the amount of heat transported is calculated by multiplying the temperature difference between the supply and return flow by the volume of water that has flowed through. Let's take an example: if hot water at 70°C flows into a flat and comes back at 50°C, a temperature difference of 20 Kelvin was used for heating. The greater this difference and the more water flows through, the more energy is consumed.
Why is precision so important?
Even small measurement inaccuracies can have a big impact. This is illustrated by the following example: at a typical temperature difference of 20 Kelvin, a measurement error of just 0.1 Kelvin results in a 0.5% deviation in the consumption bill. With annual heating costs of €2000, that would already be a difference of €10.
The principle of probe pairs
Two precisely matched temperature probes are always required for a precise measurement. Thanks to our automated pairing process, we achieve minimal deviations between the probes:
- Systematic errors are largely eliminated by pairing
- The measurement accuracy is maintained over the entire service life
- Each probe pair receives a label that includes all approval-related data as well as the measured values of the pairing in a QR code.
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Why are heat and cold meters needed?
How do the requirements for heat and cold measurement differ?
The main differences are:
Heat measurement:
- Typical measuring range: 0°C to +150°C
- MID approval required
- Direct installation required as standard
Cold volume measurement:
- Extended measuring range: -50°C to +150°C
- National approvals required
- Special requirements for condensate protection
- Immersion sleeve installation often preferred
How is heat consumption measured?
The measurement of the heat energy consumed is based on two core components: the flow meter continuously records the amount of water flowing through the system. At the same time, precise temperature sensors measure the exact water temperature in both the supply and return lines. The heat energy actually consumed is calculated from the difference between these temperatures and the amount of water that has flowed through.
What should I look out for when choosing?
Technical aspects
- Compatibility with the heat meter used
- Required cable lengths (max. 2.5m for Pt100, 12.5m for Pt500, 25m for Pt1000)
- Installation situation (direct installation or immersion sleeve)
- Special requirements (e.g. cooling measurement, aggressive media)
Legal requirements
- Current approvals for the area of application
- Legal requirements for calibration
- National specifics in D-A-CH
- Documentation requirements
Installation and assembly
Direct installation
- Prescribed for new systems up to qp 6
- Assembly according to DIN EN 1434-2
- Observe the minimum immersion depth ≥ 20 mm
- Ensure correct sealing
Immersion sleeve installation
- Only with listed immersion sleeves (existing immersion sleeves on the list of accepted immersion sleeves from the PTB)
- Use heat transfer paste
- Ensure thermal coupling
- Documentation of the immersion sleeve used
Installing the probes requires care and expertise. Here are some proven practical tips:
Make sure you use the correct installation depth. The probe tip must be in the center of the flow – comparable to a paddle that must be properly immersed in the water to be effective.
Professional installation is crucial for measurement accuracy. We support you with:
- Detailed installation instructions
- Technical drawings for all variants
- Compatibility lists for immersion sleeves
- Training documents for your technical team
Which mounting options are approved and what advantages do they offer?
There are three approved mounting options:
1. Direct installation (DS):
- Optimum response time
- Lowest measurement uncertainty
- Required for new plants up to qp 6
2. Installation in approved thermowells:
- Replacement without draining the system possible
- Protection against aggressive fluids
- Use only with listed thermowells
3. Universal version (DS/PS):
- Maximum flexibility
- For special installation situations
- Can be combined with various connection fittings
What designs are available?
We offer three coordinated product lines:
- Fast response temperature probe for direct installation (DS) guarantee particularly short response times when the temperature changes thanks to their optimized design. This makes it possible to measure consumption even more accurately. (Available on request)
- Temperature probe (pair) direct installation (DS)) are the classic solution for most standard applications. They combine high measurement accuracy with a robust design. (Available directly from the shop)
- Temperature sensors for universal use (DS/PS) offer maximum flexibility in installation and are also suitable for special installation situations. (Available on request)
Selecting the right probe is like choosing the right tool. Different tasks require different solutions:
Our classic direct-installation probe is suitable for standard applications in heating systems. It combines robustness with high accuracy – comparable to a high-quality universal tool.
In systems with rapid temperature changes, such as in fresh water stations, we recommend our fast-response variant. It detects temperature fluctuations particularly quickly – like a precision instrument.
Our temperature sensors are characterized by the following features:
The measuring ranges are optimally matched to the application and, depending on the design, cover temperatures from -50°C to +150°C. The limit value of the temperature difference is 3K. The response times are exceptionally short, with up to ≤ 1 second for our fast-responding temperature probes, depending on the sleeve diameter. This enables particularly precise detection, even with rapid temperature changes. Pt100, Pt500 and Pt1000 sensors are available as measuring elements, all in class B according to EN60751. The IP65 protection class ensures reliable operation even under demanding environmental conditions
Frequently asked questions about temperature sensors for energy meters
Which current approvals do the temperature sensors offer?
Our sensors have:
- EU type examination certificate according to MID for heat meters
- National approvals for cooling measurement (DE/AT/CH)
- Quality assurance certificates according to module D
- Entry in the list of approved existing thermowells
How long are the calibration periods?
- Heat meters: 5 years
- Cold meters: 5 years
- The period begins with the year of the conformity assessment.
- If the calibration mark is damaged, immediate replacement is necessary.
Which heat meters are the probes compatible with?
Our temperature probes can be used universally with all standard heat meters that use Pt100, Pt500 or Pt1000 sensors in a two-wire design.
What are the maximum cable lengths?
- Pt100: maximum 2.5 m
- Pt500: maximum 12.5 m
- Pt1000: maximum 25 m
These values apply when using our standard cables with a cross-section of 0.22 mm² in a 2-wire design.
What sleeve diameters are available for heat meters?
There are typically three sleeve diameter increments:
Fast-responding temperature sensors are also available in stepped versions.
Can existing immersion sleeves continue to be used?
- Only if they are included in the current list of approved devices.
- Compatibility must be documented.
- A passport test report is required.
- Thermal coupling must be ensured.
What installation options are permitted?
The following are permitted:
- direct installation (DS) – optimal for new systems
- thermowell installation (PS) – with listed thermowells
- universal version (DS/PS)
What must be observed during installation?
- Observe minimum immersion depth ≥ 20 mm
- Use the supplied seals
- Observe tightening torques (4 Nm for process connection)
- Sealing according to regulations
How can defective temperature sensors be recognized?
Typical signs are:
- Implausible temperature readings
- Strongly fluctuating measured values
- No temperature difference despite flow
- Error messages on the heat meter
- Visible damage
What needs to be documented when replacing a sensor?
Required documentation:
- Old and new serial numbers
- Pairing certificates
- Declarations of conformity
- Installation protocol with photos
- Seal documentation
Which heat meters are the sensors compatible with?
Our temperature sensors are universally applicable and compatible with all common heat meters that use the following sensors:
- Pt100 (100 Ohm at 0°C)
- Pt500 (500 Ohm at 0°C)
- Pt1000 (1000 Ohm at 0°C)
The two-wire connection technology corresponds to the industry standard
What documentation must be prepared for the calibration authority during installation?
The following documents are required:
- declaration of conformity of the temperature sensors
- matching certificate with serial numbers
- Installation protocol with details of the type of installation
- Documentation of the sealing
- For immersion sleeves: Proof of listing in the tolerance list
How is the measuring accuracy of the temperature sensors ensured?
Our quality assurance includes:
- 100% inspection of each individual sensor in the factory
- Automated pairing process with digital documentation
- Traceable calibration to national standards
- Continuous production monitoring according to module D
- Regular audits by the notified body
What special requirements are there for integration into existing systems?
When integrating into existing systems, please note:
- Checking the existing installation situation (thermowells/direct installation)
- Compatibility check with the installed heat meter
- Observing the maximum permissible cable lengths
- Documentation of the change for the calibration authority
- If necessary, adaptation of the measuring point equipment
Which current normative developments must be observed?
Important current aspects:
- Implementation of the MID directive 2014/32/EU
- National specifics in D-A-CH
- Development of cooling meter standardization
- New requirements for cyber security
- Trends in remote reading
What is the service life for which temperature sensors are designed?
- Technical service life: at least 15 years
- Approval certificate for two calibration cycles
- Designed for long-term temperature exposure in the specified range
- Resistant to changing temperatures and ambient humidity
- Vibration-resistant
- Long-term stability of measured values thanks to high-quality sensors
When must temperature sensors with approval be used?
- For all billing-related measurements (statutory requirement)
- In heating systems with multiple users
- In district heating transfer stations
- In commercial properties
