Building Services

Building Services for Architects

Section 1: HVAC Systems for Architects

Mechanical ventilation, heating, and cooling systems are the single largest consumer of building volume after the primary structure. The architect's HVAC decisions at concept stage — system type, plant room location, riser positions, ceiling void depth — are largely irreversible. This section equips architects to make informed selections and understand spatial consequences.

Space Allowances: Mechanical Plant as Percentage of GFA

System Type 1: Natural Ventilation

• Description: Relies on wind-driven and buoyancy-driven airflow through operable windows, trickle vents, and/or ventilation shafts. No mechanical cooling. Heating by radiators, underfloor heating, or convectors.
• Spatial impact on architecture:
  • Floor plate depth: Maximum 12-15m (single-sided ventilation 2.5x floor-to-ceiling height; cross-ventilation up to 5x)
  • No ceiling void for ductwork — 50-150mm for surface pipework/wiring only
  • No AHU plant rooms required
  • Ventilation shafts/stacks may be required for buoyancy-driven ventilation (0.5-1.5m² per stack)
  • Heating plant room: 0.5-1.0% of GFA (boiler room)
• Energy performance: 0 kWh/m²/yr for ventilation energy (heating energy 30-60 kWh/m²/yr)
• Noise ratings: NR 25-35 (dependent on external noise — problematic on busy roads)
• Best-fit building types: Low-rise residential, schools (in temperate climates), low-rise offices in rural/suburban settings
• Limitations: Cannot control humidity. Dependent on external conditions. Not suitable for deep plans, noisy sites, polluted environments, or climates with sustained temperatures above 28C.

System Type 2: Mixed-Mode / Hybrid Ventilation

• Description: Natural ventilation used when external conditions permit; mechanical ventilation and cooling activated when natural ventilation is insufficient. Requires automated facade (actuated windows/louvres) and BMS integration.
• Spatial impact on architecture:
  • Floor plate depth: 12-18m (wider than pure natural vent due to mechanical backup)
  • Ceiling void: 200-400mm (reduced ductwork for supplementary mode)
  • AHU plant rooms: 1.5-3% of GFA
  • Riser shafts: Smaller than fully air-conditioned — 0.5-1.0m² per floor per riser
• Energy performance: 40-70 kWh/m²/yr (total HVAC energy), 30-50% less than full air conditioning
• COP: Variable — depends on proportion of mechanical operation
• Best-fit building types: Offices (progressive clients), universities, libraries, civic buildings
• Exemplar: The Hive, Worcester (2012); Bloomberg HQ, London (2017)

System Type 3: Fan Coil Units (FCU) + Fresh Air

• Description: Centralised fresh air supply (via AHU) provides ventilation air only (typically 10-12 L/s per person). Individual fan coil units at ceiling level provide local heating/cooling using chilled/hot water from central plant. 4-pipe system (separate heating and cooling circuits) is standard for commercial buildings.
• Spatial impact on architecture:
  • Ceiling void: 350-500mm (AHU ductwork: 300-400mm rectangular; FCU: 200-300mm high; pipework: 100-150mm)
  • AHU plant room: 2-3% of GFA
  • Chiller plant (roof or basement): 1-2% of GFA
  • Riser shafts: 0.5-0.8m² per floor (4 pipes + fresh air duct)
  • FCU access panels in ceiling: 600x600mm per unit, at 3-6m spacing
• Ductwork dimensions: Fresh air main duct: 400x300mm to 800x400mm (depending on floor area served). Branch to each FCU: 200x150mm flex duct.
• Pipework dimensions: CHW/HHW mains: 50-100mm diameter. Branch to FCU: 15-22mm diameter.
• Energy performance: COP 3.5-5.0 (chiller). Total HVAC energy: 80-120 kWh/m²/yr.
• Noise ratings: NR 35-40 (FCU noise can be problematic in quiet spaces — specify low-noise units)
• Best-fit building types: Hotels (individual room control), residential apartments (with central plant), commercial offices, hospitals (patient rooms)

System Type 4: Variable Air Volume (VAV)

• Description: Centralised AHUs supply conditioned air through a duct network. VAV terminal boxes at each zone modulate airflow volume to match heating/cooling demand. High airflow rates require large duct sizes.
• Spatial impact on architecture:
  • Ceiling void: 500-800mm (large main ducts: 600x400mm to 1200x600mm; branch ducts: 300x250mm to 500x300mm; VAV boxes: 300x400x800mm)
  • AHU plant room: 3-5% of GFA (AHUs are large: typical unit 2.0x1.5x3.0m serving 1000-2000m²)
  • Riser shafts: 1.0-2.0m² per floor (large supply and return air ducts)
  • Return air: Via ceiling plenum or ducted return (adds to void depth if ducted)
• Ductwork dimensions: Main supply duct: 800x400mm to 1500x800mm. Branch ducts: 300x200mm to 600x300mm. Return air duct: 70-80% of supply duct size.
• Energy performance: COP 3.5-5.5 (chiller). Fan energy significant — variable speed drives reduce this by 30-50%. Total HVAC energy: 90-140 kWh/m²/yr.
• Noise ratings: NR 30-40 (well-designed); NR 40-50 (poorly designed — duct velocity critical)
• Best-fit building types: Large open-plan offices (>2000m² per floor), laboratories (high air-change rates), clean rooms, trading floors
• Limitations: Large duct sizes increase floor-to-floor height. Not efficient for cellular offices with many small zones. Higher fan energy than water-based systems.

System Type 5: Chilled Beams (Active and Passive)

• Description: Chilled water circulates through finned tubes mounted in ceiling-level units. Passive chilled beams rely on natural convection. Active chilled beams induce room air over the coil using a primary air supply from a central AHU.
• Spatial impact on architecture:
  • Ceiling void: 300-450mm (active chilled beams: 200-300mm high + primary air duct 150-200mm)
  • AHU plant room: 2-3% of GFA (smaller AHUs than VAV — primary air only)
  • Riser shafts: 0.6-1.0m² per floor (CHW pipes + primary air duct)
  • Chilled beam units: 300-600mm wide x 1200-3000mm long, mounted flush in ceiling grid or exposed
• Pipework dimensions: CHW mains: 40-80mm dia. Branch to beam: 15-22mm dia. Primary air duct: 250x200mm to 500x300mm.
• Energy performance: Excellent — water transports 4x more energy per unit volume than air. COP 4.0-6.0. Total HVAC: 60-90 kWh/m²/yr.
• Noise ratings: NR 25-30 (passive beams are silent; active beams have slight induction noise)
• Best-fit building types: Offices (premium), schools, universities, museums — where quiet operation and low energy are priorities
• Limitations: Condensation risk — chilled water temperature must stay above dew point (typically 14-16C). Not suitable for high latent loads (kitchens, swimming pools). Limited cooling capacity: 80-120 W/m² (vs 150+ W/m² for FCU/VAV).

System Type 6: Variable Refrigerant Flow (VRF/VRV)

• Description: Direct expansion refrigerant system with one outdoor condensing unit serving multiple indoor fan coil units via refrigerant pipework. Heat recovery variants (3-pipe) allow simultaneous heating and cooling in different zones.
• Spatial impact on architecture:
  • Ceiling void: 250-350mm (indoor units: 200-250mm high; refrigerant pipes: 15-30mm dia.)
  • No central AHU plant room required (massive space saving)
  • Outdoor condensing units: roof or ground level, 800x300x900mm each (3-6 per system)
  • Riser shafts: Small — 0.2-0.4m² per floor (refrigerant pipes only; separate fresh air required)
  • Fresh air provision: Separate DOAS or heat recovery ventilation unit required
• Refrigerant pipework: Liquid line 6.35-15.88mm dia.; gas line 12.7-28.58mm dia. Maximum pipe run: 165m (varies by manufacturer).
• Energy performance: COP 3.5-5.5. Total HVAC: 70-110 kWh/m²/yr.
• Noise ratings: NR 30-35 (indoor units); outdoor units can be 55-65 dBA (screen or locate away from noise-sensitive facades)
• Best-fit building types: Multi-zone buildings (offices with diverse tenants), retrofit (small pipes suit existing buildings), hotels, residential with individual metering
• Limitations: Refrigerant charge limits in occupied spaces (F-gas regulations). Maximum pipe lengths limit building size. Not suitable for very large floor plates. Refrigerant leak detection required.

System Type 7: Displacement Ventilation

• Description: Low-velocity conditioned air supplied at floor level (or low-level wall diffusers) rises naturally through buoyancy as it absorbs heat from occupants and equipment. Extract at ceiling level. Creates stratified temperature profile — cooler at occupied level, warmer at ceiling.
• Spatial impact on architecture:
  • Raised floor: 250-400mm (supply air plenum beneath raised floor)
  • Ceiling void: 200-300mm (return air only — smaller than conventional systems)
  • Floor diffusers: Swirl-type, 200-300mm diameter, at 4-6m² per diffuser
  • AHU plant room: 2-3% of GFA
• Ductwork dimensions: Underfloor supply through raised floor plenum — no supply ductwork above ceiling. Return ducts at ceiling: 400x300mm to 600x400mm.
• Energy performance: 15-30% more efficient than overhead mixing ventilation. Supply air temperature 18-20C (vs 12-14C for mixing). Total HVAC: 55-85 kWh/m²/yr.
• Noise ratings: NR 25-30 (very quiet — low air velocities)
• Best-fit building types: Auditoria, theatres, concert halls (seated audience generates buoyancy), open-plan offices with raised floors, atriums
• Limitations: Supply air temperature limited to 18C minimum (drafts if colder). Cooling capacity limited: 40-60 W/m². Not suitable for spaces with high ceilings and no thermal stratification benefit.

System Type 8: Dedicated Outdoor Air System (DOAS)

• Description: Centralised AHU handles 100% outdoor air (ventilation), conditioning it to neutral temperature and humidity. Separate systems (radiant ceiling, chilled beams, fan coils, active chilled slab) handle local heating/cooling loads. Decouples ventilation from thermal conditioning.
• Spatial impact on architecture:
  • DOAS AHU: Smaller than conventional AHU (ventilation air only) — 1.5-2.5% of GFA for plant
  • Ceiling void: Dependent on local system (radiant: 100-200mm; chilled beams: 300-450mm)
  • Riser shafts: DOAS duct + local system pipework — 0.6-1.2m² per floor
• Energy performance: Total HVAC energy: 50-80 kWh/m²/yr (when paired with radiant system)
• Best-fit building types: High-performance offices, Passivhaus-adjacent designs, any building targeting ultra-low energy
• Exemplar: Bullitt Center, Seattle (2013); One Angel Square, Manchester (2013)

System Type 9: District Heating and Cooling

• Description: Thermal energy supplied to buildings from a centralised district energy plant via underground insulated pipes. Buildings connect via heat exchangers in a plant room (energy transfer station, ETS).
• Spatial impact on architecture:
  • No boiler or chiller plant on site (major space saving: eliminates 2-4% of GFA)
  • ETS plant room: 0.5-1.0% of GFA (heat exchangers, pumps, meters)
  • Underground pipe entry point required at basement/ground level
  • Distribution within building: Standard LTHW/CHW pipework from ETS
• Energy performance: Varies by district source — CHP 80-90% efficiency; waste heat recovery can be near-zero carbon; ground-source heat pump networks COP 3.5-5.0
• Best-fit building types: Urban mixed-use developments, campus developments (universities, hospitals), masterplan-scale projects
• Exemplar: Copenhagen district heating (serves 98% of city); Olympic Park London (2012); Battersea Power Station redevelopment

---

Section 2: Plumbing and Drainage

Hot and Cold Water Distribution

Cold water supply systems:

• Direct system: Mains pressure to all outlets. Typical in low-rise residential. Incoming main: 25-32mm (house), 50-80mm (apartment block), 80-150mm (commercial).
• Indirect system: Mains fills roof-level storage tank; outlets fed by gravity. Provides storage for peak demand and pressure regulation. Tank sizing: 115 litres per person per day (office); 135 litres per person per day (residential).
• Boosted system: Pumped supply for tall buildings where mains pressure insufficient. Break tanks at basement; booster pumps; roof tanks or pressure vessels at upper levels. Pressure zones every 30-40m of height.

Hot water systems:

• Point-of-use heaters: Electric instantaneous or small storage (6-15 litres). Minimal pipework. Suit remote outlets.
• Centralised calorifier: Storage vessel heated by boiler or heat pump. Capacity: 40-60 litres per person (residential); 5-10 litres per person (office). Located in plant room.
• Plate heat exchanger + thermal store: More efficient than calorifier. Common in district heating connections.
• Legionella prevention: Store hot water at 60C minimum, distribute at 55C minimum, return at 50C minimum. Dead-legs must be <3m or have trace heating.

Pipe Sizes (Typical)

Drainage Systems

Soil drainage (foul water — WCs, urinals):

• WC branch: 100mm diameter (min. 1:40 gradient or steeper)
• Soil stack (vertical): 100mm diameter (serves up to 10 floors of residential)
• Building drain (horizontal below ground): 100-150mm (1:40 to 1:80 gradient)

Waste drainage (basins, showers, sinks, baths):

• Individual waste pipe: 32mm (basin), 40mm (bath/shower/sink)
• Waste branch: 50mm (multiple outlets)
• Combined waste/soil stack: 100mm (if receiving both waste and soil)

Rainwater drainage:

• Roof outlet sizing: Based on rainfall intensity (75mm/hr UK design standard; 150mm/hr tropical)
• Downpipe: 75mm (up to 55m² roof), 100mm (up to 130m² roof), 150mm (up to 300m² roof)
• Siphonic drainage: Higher capacity at smaller pipe sizes but requires specialist design. 56mm siphonic pipe equivalent to 100mm conventional.

Drainage Falls

Wet-Room Stacking Principle

Bathrooms, kitchens, and other wet rooms should be stacked vertically through the building to minimise horizontal drainage runs. Horizontal drains require falls (25-40mm per metre) which consume floor void depth. Non-stacked wet rooms create:

• Longer pipe runs
• Deeper floor voids to accommodate falls
• More penetrations through structural elements
• Greater risk of leaks above occupied spaces

Design rule: All wet rooms should be within 3m horizontal distance of a soil/waste stack.

Riser Sizing

---

Section 3: Electrical Systems

Power Distribution Hierarchy

1. Incoming supply: From utility transformer or on-site substation. Voltage: 400V 3-phase (UK/EU) or 480V 3-phase (US). Incoming cable: typically via underground duct to main switchroom at ground/basement level.
2. Main switchboard (MSB): Located in main electrical switchroom. Distributes power to sub-main distribution boards via vertical bus-bar risers or cable risers.
3. Sub-main distribution boards: Located on each floor (or every 2-3 floors in residential). Size: typically 800x2000mm wall-mounted panel.
4. Final distribution boards: Local to each tenancy or zone. Feed final circuits (lighting, small power, dedicated equipment).
5. Final circuits: Ring mains (UK: 32A, serving 100m² floor area) or radial circuits (US: 20A, serving 50-80m² floor area).

Typical Electrical Loads by Building Type

Emergency Power

• Standby generator: Diesel generator providing backup power during mains failure. Sizing: 30-50% of building total load (life safety + critical systems). Location: basement or roof (with fuel storage, exhaust flue, acoustic enclosure). Space requirement: 1.0-2.5m² per 100 kVA. Typical office generator: 200-500 kVA (5-10m² generator room).
• Uninterruptible Power Supply (UPS): Battery backup for zero-interruption supply to critical loads (IT, medical equipment, security). Typically 5-30 minutes autonomy. Battery room: 0.5-2.0m² per 100 kVA.
• Essential circuits: Life safety lighting, fire alarm, smoke extract fans, firefighting lift, sprinkler pumps — must have secondary power supply (generator or battery).

Lightning Protection

• Requirement: BS EN 62305 risk assessment determines need. Generally required for buildings over 20m, buildings with high occupancy, or buildings with sensitive equipment.
• Components: Air termination network (roof conductors at 10-20m mesh), down conductors (at 10-20m spacing around perimeter), earth electrodes (ring earth at foundation level).
• Spatial impact: Down conductors run inside or outside the facade — coordinate with cladding design. Test clamps required at 1.5m above ground level.

Electrical Riser Sizing

Lighting Power Density Targets (ASHRAE 90.1 / CIBSE)

---

Section 4: Vertical Transportation

Elevator Types

Elevator Sizing Formula

Number of elevators required:

n = (P x RTT) / (300 x HC)

Where:

• P = peak population to be served (typically 80% of building population arriving in 5 minutes for office)
• RTT = Round Trip Time in seconds (time for one complete cycle: loading + travel up + stops + unloading + travel down)
• 300 = 300 seconds (5-minute peak period)
• HC = Handling Capacity per car (typically 80% of rated capacity — e.g., 80% x 21 persons = 17 persons for a 1600kg lift)

RTT estimation (simplified): RTT = 2 x H/V + (S x ts) + 2 x P x tp

Where:

• H = total travel height (m)
• V = rated speed (m/s)
• S = number of stops (probable) — approximately N x (1 - ((N-1)/N)^P) where N = number of floors
• ts = stop time (door open + close + acceleration/deceleration) ≈ 8-12 seconds
• P = passengers per trip
• tp = passenger transfer time ≈ 1.2 seconds

Target performance (BCO standard for UK offices):

• Waiting interval: <25 seconds (Grade A office); <30 seconds (Grade B)
• Handling capacity: 12-15% of building population in 5 minutes
• Time to destination: <90 seconds (including wait)

Elevator Shaft Dimensions

Notes: Shaft dimensions include structural walls (150-200mm concrete each side). Counter-weight space at rear of shaft. MRL lifts require slightly taller headroom (add 400-600mm) but eliminate machine room.

Escalator Dimensions

Planning rule: For floor-to-floor height of 4000mm at 30 degrees: horizontal length ≈ 4000/tan(30) = 6930mm + 1600mm run-outs = 8530mm total plan length.