Ventilation Decisions

9am – 3pm MHRV from conservatory to outside. Thermostatically controlled as well as timer. Located about 1m from ground level to preserve heat inside.

10am – 4pm MHRV from house to outside. Thermostatically controlled as well as timer. Located about 1m from ground level to preserve heat inside. 200ft³ exchange over this period, (say) 5 hours @ 40cfm

5pm – 10pm Inlet from conservatory blows hot air into house using simple heat transfer fan (Thermostat in case of house being hotter than conservatory). Inlet located about 4m from ground level to capture hottest air. Outlet at floor level. Thermostatically controlled as well as timer. (say) 5 hours @ 40cfm. Heat transfer fan from guest bedroom ceiling to dining area.

10pm – 8am Bedrooms exchange air with lounge. Located 2.4m from ground to ensure air is warm. Ecowindow unit (or thehvacshop.co.nz/products/grid?category=109) in each bedroom on a timer. Inlet and exhaust into the lounge area (Not side by side).

House air = 1,000m³ (= 1,000,000l) Each person (4) requires 10l/s = 2,400l/h. Equals 417 hours of air available. Replacement by MHRV during the day has to equal 24 x 2,400l = 60,000l/day = 200ft³. 200ft³in (say) 5 hours = 40cfm minimum.

Overhang area is 2m wide. 15m long. 1m to 2.5m height. This equals 52,000l heat storage.

May need a chimney to vent excess hot air during summer. Needs coupled with inlet vent at floor level on opposite end of conservatory. The chimney effect and cold air draw is passive. Only the opening is powered.

Thermal mass – Based on rule of thumb – 3x Area of solar glazing at 100mm thick. Say 4m roof, 1m wall glazing x 15m length = 75m². So 225m³ surface area. Floor = 90m³, so

64 btu’s per sq² of north facing glass. Concrete stores 30 BTU per ft³ per ⁰F

<12kw/day heat required to meet passive house standard.

Wet rooms and Kitchen have humidity triggered MHRV. As close as possible to source. Humidity sensitive ventilation systems (Lunos Nexxt or aereco.com/ventilation/humidity-sensitive-ventilation) automatically adjust the airflow depending on the room humidity, without electricity. It still regarded as a major technological breakthrough in demand-controlled ventilation. Filtration hard to implement on MEV. No ducting required on MEV. Intelligent air inlets, make the MEV B more efficient than the MEV A.

Mechanical extract fans (including associated ducting) must have a flow rate not less than:

25 L/s for showers and baths, and
50 L/s for cooktops.

Lunos Nexxt

Nexxt is controlled via humidity or temperature sensors as a standard and optionally also via a CO2 sensor

Volume Flow 15 – 110 m3/h
Voltage 230V / 50 Hz
Power Consumption 5W @ 15m3/h
Heat Recovery Up to 90%
Sound Power Level 20dB up to 30m3/h
Clean air using standard M5 filters with the option to increase to M7 or M9 for bacteria filtration
USB port for firmware updating, allowing to add wireless sensors, motion detectors and switches
Capability to connect to WiFi e.g. via smartphone application control
Intelligent automatic sensing of humidity and temperature as standard

Extractor fan above, on timer >50cfm

Pre-Primed – $40 for 150mm extractor fan

Table of Contents

Ducting

Flexible Ducting Pack Semi Rigid 3M x 150mm $45

tradedepot.co.nz/flexible-ducting-semi-3m-150mm

Tube 150Ø 1.2m 24g Galvanised $46

thehvacshop.co.nz/products/view/72

PVC duct round TUBE 150dia x2.5 long $103 smooth-air.co.nz/product/catalog/1.Duct*2PVCducting*

Select the largest size ducting possible as the larger the ducting diameter, the better the airflow performance and the lower the airflow noise.

A typical duct size is 200 mm diameter, which should be used wherever possible, reducing to 150- or 100-mm diameter ducting to the ceiling vents or grilles if required.

For example:

A 100 mm ceiling vent can supply sufficient fresh air to a room with an internal volume of 40 m3, for a larger room, both exhaust and supply ceiling vents or grilles should be a minimum 150 mm diameter – alternatively, two or more 100 mm diameter ceiling vents could be used.

Ducting should:

have internal surfaces that are as smooth as possible to minimise air flow resistance
have the minimum number of bends possible
where bends are unavoidable, have them as large diameter as possible
have no tight bends as these can cause significant air flow resistance
be insulated to reduce heat loss and duct noise
have a condensate drain for the exhaust ducting to allow the removal of moisture created when the heat is removed from the air.