Water-glycol/water heat pump: the case for horizontal ground loops

Understanding how a water-glycol/water heat pump with horizontal ground loops works

The refrigeration cycle explained simply (evaporator, compressor, condenser)

A water-glycol/water heat pump works like a refrigerator in reverse. In the evaporator, the refrigerant picks up heat delivered by the glycol circuit. The compressor "boosts" this fluid, raising both its pressure and its temperature. In the condenser, this heat is transferred to the heating water, and the fluid then heads back for another round.

The role of the glycol fluid and the buried loop: what you're actually recovering from the ground

The buried horizontal loop circulates a water-glycol mix, useful against freezing. As it passes through the ground, it picks up gentle, steady heat, even in winter. This energy isn't "burned" — it's simply transferred to the machine, which concentrates it to feed underfloor heating or low-temperature radiators.

Key differences from an air/water heat pump and vertical-borehole ground source

Compared with an air/water system, ground collection is more discreet and avoids losses linked to cold air. In return, it needs floor space and earthworks. Compared with vertical boreholes, horizontal loops usually cost less to install, but depend more heavily on available space and ground conditions.

Horizontal ground loops: installation conditions and points to watch on site

Available area, depth and spacing: the orders of magnitude to respect

For a ground-source heat pump on horizontal loops, plan for open ground accessible to machinery. Loops are typically laid between 0.6 and 1.2 m deep, below the frost line. Keep regular spacing between pipes (often 0.5 to 0.8 m) to limit interaction between loops. The laying area is sized according to power output and ground type. Have the layout and loop lengths validated on plan from the outset.

Soil type, moisture, earthworks: how to secure performance

Moist, homogeneous soil exchanges heat better than very dry or disturbed ground. Avoid over-drained zones, heterogeneous backfill and future heavy-load traffic. During earthworks, take care with the bedding layer. Fine sand or sieved soil, no lumps. Backfill in layers and compact without crushing the pipes. Aim for a clean install — that's the basis of performance.

Preventing issues: freezing, crushing, unbalanced loops, network locating

Think about site safety. Locate existing networks before digging. Protect the pipes from UV, impacts and pinching. Balance the loops (similar lengths, accessible manifolds) to avoid uneven flow. Tightness check, purge, then photo records and an as-built plan. Marking the ground avoids accidental re-digging later.

The advantages of horizontal ground loops: concrete arguments for your client

Geothermal stability: comfort, performance and operation in extreme cold

With horizontal ground loops, your heat pump draws heat from ground that stays at a far more stable temperature than the air. The result is steady comfort in the home and a performance level that drops less when it freezes. The client gets gentle heat, with no jolts, even in severe cold.

Silence and integration: a discreet solution when the outdoor space is constrained

No outdoor unit with a fan. It's often very discreet in terms of noise and façade impact, useful in housing developments, near property boundaries, or when neighbours are sensitive to noise. Outside, everything is buried. The garden stays usable, once the earthworks zones have been marked out.

Durability and maintenance: what wears, what doesn't, and what you check

Buried collectors are passive networks with no moving parts. What wears is mainly the heat pump itself, like any machine. Your lever is minimal but regular maintenance. Tightness check, pressure, fluid quality, circulators and settings. The client invests in a system built to last.

Sizing and best practices for a high-performing heat pump

Home needs: heat loss, emitters, flow temperature and heating regime

The starting point is a room-by-room heat-loss calculation. Good sizing means power output matched to the local climate, insulation level and air renewal. Also check the emitters. Underfloor heating and low-temperature radiators allow a lower flow temperature, so a more efficient heat pump. To go further, use the method for sizing a heat pump's power output.

Horizontal ground-loop length and flow rate: avoiding undersizing and overspend

In horizontal ground-source systems, the right loop length avoids stressing the ground by the end of winter. Too short, and the heat pump loses performance and may switch to backup. Too long, and earthworks get expensive. Validate flow rate and delta T on the collector side, as well as heat-transfer fluid quality.

Commissioning and settings: balancing, heating curve, circulators, temperature monitoring

Commissioning makes the difference. Fine-tuned settings: circuit balancing, heating-curve configuration, circulator speed and flow/return temperature checks. Watch for short cycling and adjust the curve rather than raising the setpoint. Monitoring during the first week secures both comfort and consumption.

Support schemes and the 2026 framework: what to check for your files

MaPrimeRénov' and CEE in 2026: documents to provide and common blocking points

In 2026, rejections often come down to details. Quotes and invoices must be consistent and complete, with product references, performance data and areas. Add the sworn statement, proof of identity and occupancy, bank details, and proof of income when required. On the CEE side, watch the dates. No signature and no invoice before commitment. A poorly worded description of the work, and the file stalls. To go further, see our article on avoiding MaPrimeRénov' file rejections.

RGE and compliance requirements: traceability of the work and site documents

Check the RGE certification's validity at the signing date, for the right scope. Keep the evidence. Before, during, after photos. Technical data sheets, labels, delivery notes. Commissioning report and settings. With simple traceability, you secure support payments, inspections, and client sign-off.

Energy audit and coherence of the approach: when the heat pump makes sense in the renovation pathway

A heat pump works better when the home loses less heat. The audit helps prioritise. Insulation and airtightness first, then sizing, emitters, controls. If the audit shows an energy-class jump with a coordinated set of measures, the file clears more easily and performance follows in real-world use.