Thank to Alan Belson for the following, from his on-going house renovation:
This ventilation system handles all the required airchanges for the whole house, and can deliver 200+ cubic metres of fresh air per hour, [117 cubic feet per minute], which in my case will change all the air in the house about every 2 hours. The fan unit consists of a pair of balanced fans coupled to an integral X-pass heat exchanger. Air extracted from the house donates heat to the fresh air entering, at an efficiency of around 85%. Air is 100% changed, there are no by-pass ducts.
On a winter's day with outside air at 32F and inside temperature at 68F, the unit saves around 1kw [3400btu/hr] in ventilation heat losses. Since the house is super-insulated, with 8" minimum of glass wool, this represents about a 30% reduction in the total furnace load.
Control is by a remote switch, giving normal, boost and extract-only modes. The fan motors run from a transformer having multiple tappings, 80v-100v-120v-140v-180v -230v, which I need to hardwire, [factory set at minimum]. 230v is for boost. The 'normal' volts have yet to be determined and await 2nd fix so I can evaluate air flow to the respective rooms. All duct terminations can be adjusted to balance flow, which will be measured by timing the filling of large flimsy plastic bags with air with the help of my attractive young assistant, the present Mrs B.
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![[Linked Image]](https://www.electrical-contractor.net/PC/AB_CIMG0030.JPG)
Pic 1. Ventilation unit in loftspace. The unit is mounted on a plywood plate suspended from the roof timbers on polypropylene ropes. This prevents sound-drumming to the rest of the stucture; in fact the unit is now so quiet it can be barely heard running from the loft hatch. All ducts with the exception of inlet and exhaust, [extremes of pic L&R heading toward the slates], are insulated with reflective foil and 2" of glass wool. This is because they will contain warm air, as this is an unheated space above the glass quilt. Supply and return ducts are 6" bore, 10" OD, with extract ducts from individual rooms in 4" bore, increasing to 6" bore as they enter the roofspace. The pink bubblewrap/foil covers are extra insulation for the unit.
In the foreground is a large 'pre-heater' box. During operation, conditions in the heat exchanger can create condensation. This is piped out through the eaves by a condense-drain. In frosty conditions the unit has a thermostat in its inlet duct which will switch to 'extract only' mode, to protect the exchanger from icing. Alan not want this to happen, for 2 reasons!
a] 'Er Indoors wants a woodburning stove for 'ambience'. ' Extract Only ' reduces pressure in the house, which could lead to smoke/fumes entering the living space.
Carbon monoxide Bad! Oxygen Good! b] Heat recovery is most wanted when it's cold, as this is when the savings in fuel are at maximum potential. So in the box, made of chipboard lined with aluminium foil, I have fitted 3 x 240W 'tube' heaters.
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![[Linked Image]](https://www.electrical-contractor.net/PC/AB_PHTH2.jpg)
Pic 2. Tube heaters. These are designed for low level heating at floor level for WCs, cloaks, mudrooms, greenhouses etc.. Heaters are 4ft long , 230V 240Watts each, [ 60W per foot] and are wired such that they operate only when vent-fans are running, so they are always in a flow of air. Twin frost stats, high in the loft vault, are set at 1deg C, [operates 1 heater] and -7deg C, [operates the other two, temporarily ]. Trials indicate that this will prevent 'extract only' mode from operating down to minus 28deg C [ -18deg F ]. Note that even at full chat, heat recovery should still be more than the electrical consumption. A third frost stat is on order from the UK. Guess who trod in one with a size 11 boot !
This box has now been covered with a bubble/foil blanket to insulate it.
Under normal conditions, we intend this setup to operate 365/24. In summer it will also reduce the AirCon load by pre-chilling incoming air. Boost will only be used when the range is working, so that extra air is changed out when cooking- bearing in mind that the ground floor [1st] is open plan. The cooker-hood has its own grease and carbon filters, but these are duplicated in the fan-unit to protect the heat exchanger from crud. A fire-stop damper has been fitted at the cookerhood exit in case fire gets drawn into the ductwork from, say, a pan-fire. This consists of a short steel duct containing a fusible sprung-damper and intumescent seals, mounted directly to the hood exit duct. Over The Top? You bet!! We're having some real fun on this project!
