A Technical, Economic and Regulatory Case for Adopting the Correct VWATD Methodology and Daily‑Frequency Data Collection

Prepared for:

Department for Energy Security & Net Zero (DESNZ)*
Office of Gas and Electricity Markets (Ofgem)*
- Date:** May 2026

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Executive Summary

The Heat Network Technical Assurance Scheme (HNTAS) introduces a regulatory framework intended to ensure minimum performance standards across UK heat networks. A central metric within this framework is **KPI‑08**, which measures **volume‑weighted average temperature difference (VWATD)** at consumer connections.

This white paper demonstrates that:

**The correct VWATD calculation requires only cumulative energy and cumulative volume**, meaning **two readings per period** (e.g., monthly) are mathematically sufficient.
**Daily readings are more than adequate** for regulatory assurance.
**30‑minute data provides no additional accuracy** for KPI‑08 and therefore cannot be justified as a regulatory requirement.
Mandating 30‑minute data would impose **£0.5–£1.2 billion** in national infrastructure upgrade costs, compared to **<£3 million** over 10 years for a daily‑data regime.
A 30‑minute requirement would be **legally vulnerable** under UK administrative law on grounds of irrationality, disproportionality, and anti‑competitive effect.
The presence of **commercial ties between Fairheat (HNTAS technical author) and Guru Systems (a vendor of high‑frequency metering systems)** creates a **perceived conflict of interest**, increasing the importance of demonstrable technology neutrality.

Recommendation: DESNZ and Ofgem should adopt the **correct VWATD methodology** and explicitly specify that **daily cumulative readings satisfy KPI‑08**, ensuring proportionality, legal defensibility, and technology neutrality.

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1. Background: KPI‑08 and the Purpose of HNTAS

HNTAS is designed to provide **minimum regulatory assurance**, not operational optimisation. KPI‑08 measures the **return temperature performance** of consumer connections, a key determinant of network efficiency.

The KPI is intended to:

Identify persistently poor ΔT performance
Support fair comparison across networks
Provide a regulatory baseline for compliance

It is *not* intended to:

Optimise real‑time control
Provide granular operational diagnostics
Mandate specific metering architectures

Therefore, the data requirements must be **proportionate to the regulatory purpose**.

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2. The Correct VWATD Calculation

VWATD is defined as:

``` ΔT_VWATD = E / (ρ · c · V) ```

Where:

E = total energy delivered over the period
V = total volume over the period
ρ = density of water (constant)
c = specific heat capacity (constant)

Because both E and V are **cumulative meter registers**, KPI‑08 can be computed from:

Start cumulative energy and end cumulative energy
Start cumulative volume and end cumulative volume

Thus:

Only two readings per period are required.

Daily readings are therefore **more than sufficient**, and 30‑minute readings provide **no improvement** in KPI accuracy.

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3. Data Frequency Requirements: Daily vs 30‑Minute

3.1 Mathematical sufficiency

Monthly readings → fully sufficient
Daily readings → more than sufficient
30‑minute readings → no additional regulatory value

3.2 Regulatory principle

Under the Regulators’ Code and Better Regulation Framework, DESNZ must ensure:

Proportionality
Minimal burden
Technology neutrality
No unnecessary cost to consumers

A 30‑minute requirement fails these tests.

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4. UK‑Wide Cost Impact Assessment

Assuming **2 million consumer connections**.

4.1 Data platform cost difference

Frequency	Annual Data Volume	7‑Year Storage	Annual Cost	10‑Year Cost
Daily	~0.07 TB	~0.5 TB	~£5k	~£50k
30‑minute	~3.5 TB	~24.5 TB	~£245k	~£2.4m

Incremental cost of 30‑minute regime: ~£2.3m over 10 years.

4.2 Infrastructure upgrade cost

To deliver reliable 30‑minute telemetry, legacy systems require:

New gateways/head‑ends
New backhaul communications
Meter rewiring or replacement
Engineering, commissioning, documentation

Indicative costs:

Capex per connection: **£150–£400**
UK‑wide capex: **£300–£800 million**
Opex: **£20–£40 million/year** → **£200–£400 million** over 10 years

Total 10‑year cost of 30‑minute requirement:

- £500 million – £1.2 billion**

Total 10‑year cost of daily‑data regime:

- <£3 million**

Cost multiplier:

- 30‑minute requirement is 200–400× more expensive** with no improvement in KPI‑08 accuracy.

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5. Legal Vulnerability of Mandating 30‑Minute Data

A 30‑minute requirement would be vulnerable to Judicial Review on several grounds.

5.1 Irrationality

KPI‑08 can be calculated from monthly data
30‑minute data does not improve accuracy
Cost impact is £0.5–£1.2bn
Therefore the requirement is irrational

5.2 Disproportionality

Fails the Regulators’ Code because:

Burden is excessive
No regulatory benefit

5.3 Ultra vires

HNTAS is for **minimum assurance**, not operational optimisation.

5.4 Anti‑competitive effect

A 30‑minute requirement:

Favours specific vendors
Disadvantages legacy systems
Is not technically necessary

5.5 Procedural unfairness

If DESNZ fails to:

Consult adequately
Consider cost evidence
Publish an impact assessment

…the requirement is challengeable.

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6. Conflict‑of‑Interest Considerations

6.1 Documented ties

Fairheat’s Managing Director is a **co‑founder, director and shareholder** of Guru Systems.
Guru Systems sells high‑frequency, encrypted metering systems.

6.2 Relevance

A 30‑minute requirement would **commercially advantage** systems aligned with Guru’s architecture.

6.3 Perception of regulatory capture

Even without improper influence, the perception matters:

Appears vendor‑aligned
Undermines confidence in HNTAS
Increases legal risk

6.4 Importance of neutrality

Adopting the correct VWATD methodology ensures:

Technology neutrality
Market fairness
Regulatory legitimacy

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7. Recommendations

1. Adopt the correct VWATD methodology

Use cumulative energy and volume
Daily readings are sufficient
30‑minute data not required

2. Ensure proportionality

Avoid premature replacement of metering
Maintain neutrality
Minimise consumer cost

3. Publish an impact assessment

Quantify national cost
Compare daily vs 30‑minute regimes

4. Address conflict‑of‑interest concerns

Ensure transparent governance
Separate technical authorship from commercial interests

5. Provide clear operator guidance

Daily cumulative readings are compliant
Monthly readings are mathematically sufficient
30‑minute data is optional for operational optimisation

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8. Conclusion

KPI‑08 (VWATD) can be calculated accurately from **two readings per period**. Daily readings are more than sufficient. A 30‑minute requirement would impose **hundreds of millions of pounds** in unnecessary cost, provide **no improvement** in KPI accuracy, and expose DESNZ and Ofgem to **significant legal risk**.