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#123339 - 03/19/06 10:02 AM Heat Recovery Ventilation System  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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.


[Linked Image]

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.


[Linked Image]

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!

Tools for Electricians:

#123340 - 03/19/06 11:51 AM Re: Heat Recovery Ventilation System  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
I recently referred to the need we have to learn something about other trades- how their stuff works, what the components look like, etc. Paul, your pics bring this lesson home.

Gone are the days when a "sparky" could content himself simply pulling wires and hooking up devices. More and more, homes are getting rather involved control circuits in them.

Apart from fancy heat pumps and air handlers, more homes are getting indoor spas, involved lighting schemes, automated things like window shades, and generating equipment.

#123341 - 03/19/06 04:32 PM Re: Heat Recovery Ventilation System  
walrus  Offline
Joined: Jul 2002
Posts: 680
Bangor Me. USA
Very cool setup, are you doing it for fresh air or to save money, both?? Whats the cost of running the fans vs heat saved.

#123342 - 03/19/06 07:04 PM Re: Heat Recovery Ventilation System  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Walrus...I installed a massive such system for an indoor pool; as you might guess, there is a real challenge keeping the humidity down!

In that system, it was not possible to operate economically until we installed speed controls on the blowers. With them in place, we were able to reduce current draw from almost 30 amps, to less than 8 (on each of two fans).

There are perhaps other solutions ... dampers and such ... but (energy considerations aside) you are still left with the need to sort out your control wiring. We've gone beyond the sparky just running the power, and everything being self-contained in the unit.

#123343 - 03/19/06 08:06 PM Re: Heat Recovery Ventilation System  
Alan Belson  Offline
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Both fans run at 160W normal (120v tapping estimated) power. Of course 80W of that enters the house in the input stream by fan cooling, so we have a max 80W loss exhaust-fan load whether operated as heat recovery or chill recovery.
Clean air is not a problem here, very rural. Savings on fuel are the main driver, plus the need to control drafts with full underfloor heating on both levels. These systems are very low-powered [ about 5 watts per square foot floor area] and air-leakage and insulation needs to be of a high order for satisfactory operation.
Good ventilation is a must if a dwelling is to remain a healthy environment. It replaces vitiated air containing moisture, dusts, chemicals, carbon dioxide, spores, baceria, smells, etc.. How much ventilation is the question. 1 or 2 changes of air was considered necessary even a decade ago. Now, 1/3 to 1/2 an air change on a constant basis is considered sufficient. My wife is a 'throw all the windows open' sort of lady. This had to be curbed if the house was to stay warm, short of nailing up the casements! Even this low venting rate costs, especially now with high fuel prices and more coming. My plan is to vent 50% of the house volume per hour, ie 200m3 per hour, on a constant basis rather than howling-gales then nothing.
If we take air in at 0C and eject air at 21degC-

200x21x 993 joules/ x1.29kg/m3
= 5380074/3600sec = 1494W loss.
@ 85% recovery, potential savings= 1270W
There is a condensate contribution, and with Atlantic coast humidity levels, a further donation by latent heat of condensation of water vapor on the condenser plates of 300W would not be unrealistic. Here is my estimate-
0.7kg x 2,260,000/3600 = 313W

Of course, re-humidification of the drier air by electric humidifiers negates some of that gain, but there will be some.

If I get 1000W of recuperation, not an unreasonable target:

Heat cost. Diesel oil, 80% burner efficiency, @ today's oil price. is approx US 10c/kwh.
nb. I have to pay 19.6% sales tax, this is France.
Annual use taken as 6 months operation Oct-March = 4032 hours. Let mean temperature differential in that period be 10degC = 60% then say 2400 hours of recuperation would be more than feasible. As an indication, this year the temperature has hovered around an average 5deg C since before Christmas.

2400 kwh x 10c = $240 savings per year, at least.
Further unquantified savings on AIRCON operation will also accrue, but I have not calculated those. (The above data comes from my house notes.)

Payback on capital: Less than 5 years = 'earning' of 20%+. Can you get that on your savings at the bank?
I should add I also get a tax-break of 40% off my tax bill for the capital expenditure too, as an 'environment incentive'. That Chirac, he's not all bad!


Wood work but can't!

#123344 - 03/19/06 11:56 PM Re: Heat Recovery Ventilation System  
techie  Offline
Joined: May 2005
Posts: 246
palo alto, ca usa
The unit is mounted on a plywood plate suspended from the roof timbers on polypropylene ropes.

I really don't like this rigging..

I don't like using polypropylene in overhead rigging due to the cold flow characteristics of the material. I would prefer to use some other material such as polyester, nylon, or dacron.

I also hope that there are no attic windows for the rope to be exposed to UV.

The problem is that polypro can sit in place for a long time, and then fail suddenly due to alterations in the molecular structure.

#123345 - 03/20/06 01:46 PM Re: Heat Recovery Ventilation System  
JoeTestingEngr  Offline
Joined: Nov 2005
Posts: 785
Chicago, Il.
At first I wondered why Robbie the Robot was lying down in your attic. That is quite an elaborate scheme you have going there and it is clear that you've put alot of thought into it. Is there any chance that you could post some diagrams of what you've done because a few are a little fuzzy to me?

I used to watch my electric bill spike with my A/C in the summer & the humidifier in the winter. The last few winters I left the humifier in its box and pulled out two fountains instead. I also built a fountain with touch pads that my little angel uses to control LEDs shining up through the water. The evaporation from the three fountains and several plants seems to be enough to keep my place comfortable. I add at least 20 oz. of water to the 2 small fountains on a typical winter day. I had remembered reading an article about Burt Rutan humidifying his home in the California desert with a waterfall. One fountain is powered from a 9 watt wall transformer but I haven't measured its actual power consumption. The other lava fountain has a 24 watt transformer but the lamp that it used to power, immersed in water, was removed. I doubt that both together consume more than 20 watts. Are plants and/or fountains things that you and your wife would consider to reduce humidification costs?

#123346 - 03/20/06 09:45 PM Re: Heat Recovery Ventilation System  
walrus  Offline
Joined: Jul 2002
Posts: 680
Bangor Me. USA
This is a pretty cool site on buildings and how to avoid problems with mold, air quality etc and get energy savings

#123347 - 03/23/06 08:05 AM Re: Heat Recovery Ventilation System  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
From Alan:
Joe, the difficulty of manipulating 10" flex. duct in a confined space to meet up with the correct ports certainly led to a bit of complexity.

I've drawn these simple schematics up to show the arrangement. The 'Collector Box', which can just be seen in the background wrapped in pink bubble/foil, was built from chipboard to pick up the eight room extract ducts, [ wc, utility room, kitchen, range hood, lounge, 2 bathrooms (drawing air from the adjacent bedrooms), my office], as they enter the loft and allowed a single duct to run from there to the air-handler.

The electrical circuit is pretty straightforward, with simple 2 way remote switching for the 3 operation variables. The makers' electric circuit was quite poor, it took ages to decipher because it was broken up into 'mini-circuits'- you had to find the correct coded terminal elsewhere on the drawing.

The only modification immediately planned is to add a max temperature thermostat [ = say 75deg C] inside the heater box in case of fan failure, although the heaters did not get hot enough to burn your hand when run up on the bench. Better safe than sorry.

I haven't bought humidifiers yet, and we do have a lot of house plants already. That's a good idea to use plants as the water source for re-humidification.

Techie, on the point about polypropylene rope creep, quite right, I dropped a clanger there. I'll have to change to a different suspension material.

I'm not so concerned about it dropping - it's only 1" off the floor, but the base is tilted and positioned so as the candense will run away. There are no loft windows, so UV won't be a problem.

[Linked Image]

[Linked Image]

#123348 - 03/24/06 03:32 AM Re: Heat Recovery Ventilation System  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Brilliant diagrams Alan.
And a very well thought out and installed system, I hope it serves you well!. [Linked Image]
{Regulars at this forum will also remember Alan's underfloor heating system that he installed about a year or so ago, this guy knows what he is doing and a few people could take a leaf or two out of his book!}.

Let's face it, these days if you're not young, you're old - Red Green grin

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