Methodology and calculation

1Scope

The configurator and the catalogue pages provide a preliminary design for planners: outer dimensions, weight, noise reduction, an approximate assessment of noise immission, air side and wind load, and specification texts. All values are indicative.

The binding design – acoustics, pressure drop, structural – is carried out per project by our engineering team, including CFD simulation. Only the values in the project quotation are binding.

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2Noise reduction of the acoustic levels

Each acoustic level has a typical noise reduction ΔL_WA. This is the reduction of the A-weighted sound power of the unit by the enclosure. The values are typical values from completed projects; the design follows the enveloping-surface method (sound power over a measurement surface around unit or enclosure, without and with enclosure).

• These are typical values, not guaranteed minimum values. The actual reduction depends on the noise spectrum of the unit.
• For strongly low-frequency or tonal sources, the reduction is to be checked per project.
• In the calculation core the reduction is a single-number value per level and does not depend on enclosure size.
• Package recommendations include a 3 dB reserve (see section 5).

3Enclosure dimensions and weight

Design standard

Clearances from the unit to the outer edge of the enclosure:

Other clearances can be entered. If they are below the standard, a note recommends an engineering review.

Outer dimensions

• The installation height is 120 mm on a foundation with anti-vibration mounts, otherwise the entered frame height (large-equipment catalogue).
• On top (upward discharge) or at the end (side discharge) sits the silencer with height k per level:
  • Plus/Standard 600 mm
  • Pro/Premium 1,000 mm
  • Max 1,400 mm
• For low enclosures (internal height below 2 m), k is reduced proportionally, to no less than 40 %.
• PV enclosures have a field of HSA3 tubes Ø 200 mm in the roof instead of a silencer: 500 mm long (Standard) or 600 mm long (Premium, hence 900 mm top clearance).

Weight

The weight is derived from panel and silencer areas using fixed area and volume weights of the standard build-up: MiniTec aluminium profiles 45 × 45, aluminium panels, HSA3 inner lining. It is an indicative value, excluding base, anti-vibration mounts and fixings.

4Sound power with enclosure

• Several identical units are added energetically: +3.0 dB for 2 units, +4.8 dB for 3 units.
• In the catalogues, the loudest model of a series is used.

5Sound propagation and assessment to TA Lärm (configurator)

The configurator estimates the rating level at the relevant immission point and recommends an acoustic level from it.

Sound pressure level at the immission point

• Point source in half-space, r = distance in m
• K_refl: +3 dB in front of a wall, +6 dB in a corner or recess

Rating level

• K_T = tonality, 0 / 3 / 6 dB
• K_R = rest-period surcharge, daytime only in purely and generally residential areas and spa areas, continuous operation:
  • working days 10 · lg((13 + 3 · 10^0.6) / 16) = 1.9 dB
  • Sundays and holidays 10 · lg((9 + 7 · 10^0.6) / 16) = 3.6 dB

Immission guide values (outdoors, TA Lärm)

All values in dB(A).

Target value and package recommendation

• Without background noise, the target value is the guide value IRW.
• With the irrelevance criterion, the target value is IRW − 6 dB.
• With known background noise L_V:

If ΔL_req is −3 dB or below, no enclosure is likely to be needed. Above 25 dB we recommend a special design.

Not considered: ground and air absorption, screening, meteorology, short-term peaks and frequency dependence.

6Air side: velocity, pressure drop, heat

Heat pumps, refrigeration, VRF

• Intake via a louvre band around the enclosure up to half its height, at most 1.2 m, minus the doors.
• Discharge via the free cross-section of the silencer of the selected level.
• The resistance coefficients ζ of louvres and silencers are stored per level.
• The pressure drop is compared with the available external static pressure of the fans:
  • ≤ 70 % is uncritical
  • 70–100 % triggers a review recommendation
  • above that, or with v > 5 m/s, it is insufficient
• In the catalogues, the largest air flow of the series is used.
• Heat pumps, chillers, dry coolers (configurator and large-equipment catalogue): criterion v ≤ 7 m/s (large fans). No pressure-drop check in the large-equipment catalogue, as no available pressure is stored per unit.
• VRF/VRV: available external static pressure 50 Pa by default (high-static setting of the outdoor units). From 20 Pa pressure drop the result advises setting the unit to higher external static pressure; from 30 Pa the sound power of the unit is increased by 2 dB (higher fan speed).

Alternatives instead of exclusion

If a selection does not meet the air side (v > 5 m/s or pressure drop above the available pressure) or the noise target, the calculation core itself searches for designs that meet both:

• for each package (Basis to Max) the smallest enlargement of the envelope in steps of 100 mm per side, up to 1,500 mm; with side discharge the height grows as well
• pressure drop at most 90 % of the available pressure (10 % reserve), v ≤ 5 m/s or 7 m/s, rating level ≤ target; without acoustic input at least the noise reduction of the selected package
• within the optionally entered available space (max. length, width, height)
• shown are the lowest-cost, the most compact and the solution with the highest noise reduction; the noise reduction per package is kept unchanged for a larger envelope (safe side)
• if no design is found, a project-specific special solution is offered

In the catalogues (VRF; large equipment with v ≤ 7 m/s) the smallest suitable enlargement with dimensions and budget price is offered directly on the enclosure if a limit is exceeded.

PV inverters

The model with the largest heat loss in the series is used. Solar gains on the housing are not included.

7Wind load and anchoring (configurator)

The calculation is approximate to DIN EN 1991-1-4/NA with simplified peak velocity pressures q_p. The relevant height is the top edge of the enclosure, z = building height + enclosure height.

q_p in kN/m².

The partial safety factors are γ_Q = 1.5 and γ_G = 0.9. The friction coefficient is 0.4.

Valid up to z = 25 m (North Sea islands 10 m). Above that, and at edges or corners of flat roofs, a project-specific calculation is needed. The structural verification is the responsibility of the structural engineer.

8Safety factors and conservative assumptions

The noise reduction per level is a typical value. Additional safety is provided by the 3 dB reserve in the recommendation.

9Limits of validity

• Equipment: air-cooled units with axial fans (heat pumps, chillers, condensers, dry coolers, VRF), PV inverters, battery storage. Other equipment only as an indication.
• Input ranges:
  • Large equipment: length 300–15,000 mm, width and height 300–4,000 mm, 1–6 units, frame height 100–3,000 mm
  • PV: dimensions 80–3,000 mm, 1–8 inverters
• Acoustics: A-weighted single-number values, continuous operation, one immission point, free sound propagation. No forecast to ISO 9613-2 and no peak-level assessment.
• Air side: approximate via resistance coefficients, without recirculation between intake and exhaust air. The binding check is done by CFD.
• Wind load: simplified method up to 25 m height; no snow load, no seismic load, no design of fixings.
• Flammable refrigerants (A2L/A3): design notes to EN 378 and manufacturer requirements. Hazardous-area classification and risk assessment by the planner or operator.

10Worked examples

Example 1 – Heat pump in a general residential area (configurator)

Inputs:

• 1 heat pump 3,330 × 1,100 × 1,875 mm, upward discharge
• L_WA = 82 dB(A), V̇ = 36,500 m³/h, available pressure 100 Pa
• in front of a wall, immission point at 15 m
• general residential area, night, not tonal
• wind zone 2 inland, ground level

Example 2 – PV inverter, wall mounting (catalogue)

Inputs: SMA Sunny Tripower CORE2 STP 110-60, 1,117 × 682 × 363 mm, 110 kW, η = 98.6 %, front enclosure, Standard.

11Standards and regulations

The calculation is based on these standards and regulations. Listed are the editions used and the clauses the formulas in the sections above refer to. Where the configurator simplifies, the “Use” column says so.

Standards are available from DIN Media or the respective publishers. The edition in force for the project is decisive; if an edition changes in a way that affects the calculation, the calculation core receives a new version.

12Versions

Calculation core and methodology share the same version number. It is printed with the date on every “Selection as PDF” and on every design sheet of the configurator, together with the assumptions used, so you can trace which calculation state a result was produced with.