DIY - build your own ventilation system

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Starina

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#208328 7-Feb-2017 11:19

Hi everyone,

I want a positive pressure ventilation system being installed in my house. Heat recovery system won't suit as the house is not airtight and the only heatpump is not really powerfull to heat the whole house.

Got some quotes from different companies and the lowest price is around $3.3k for the ventilation system, $4k for the system with an additional 2kW heater installed (which I kind of like as it will help to heat the house during the winter time when the roof space is cold).

I think that this is quite expensive for the 'fan under the roof', that is why I would like to figure out the price for the system in case if I build it by myself.

What I've found so far:
1. Ceiling diffuser 150mm ($17 trademe, $20 Aliexpress, $20 ebay + shipping). I need 4, so aroung $100.
2. Insulated ducting 150mm x 3m ($69 in Bunnings). I need 5-6, so total is $350 - 420.
3. Filter can be used form HRV(square, $60), SmartVent($50?), MoistureMaster (round, probably the easiest to add to the non-existing system, $50)
4. Fixing/additional stuff $200.

Total is around $850 + time.

The tricky thing is with the inline fan, controller and the heater.
I was able to find some fans on Aliexpress for the price less than $50 and the airflow 530m^2/h, but they have only one speed. I think that I need at least 5 to feel comfortable.

I couldn't find any controllers and the inline heating system though.
If I am able to control the fan with ESP8266 - that would be great. No additional controller is needed in this case. I'll add a few temperature sensors and this will be enough. It's even better than to connect to an existing system.
Inline heating system should also have a few heating levels and a way to be controlled by something. Should be safe too.

Do you have any advice on finding the rest that I need for the system?
What do you think about the whole idea?
Oh, and by the way, do you know if it is possible to connect Arduino/ESP8266 to the Moisture Master controller to be able to control it from a computer?

Thanks.

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#1716444 7-Feb-2017 11:37

Our basic HRV system is either blowing on a low speed or effectively doing nothing, if you built a single speed system i would hazard a guess it would be 99.9% as useful as an equivalently specc'ed HRV with multiple fan speeds

timmmay

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#1716451 7-Feb-2017 12:01

Before we can offer much advice you should tell us why you want a ventilation system, what problem you're trying to solve. Also the kind of hours you have, and access.

A few thoughts:

The 2kw inline heater will just be heating a wire with power, far less efficient than using a heat pump 2kw won't go far for a decent sized house
Generating heat in one place and sending it to each room will lose a lot of heat, even using insulated ducting.
I'm not sure a sealed house is a requirement for a heat recovery system. Sure if it was sealed it might work a little better, but if it's blowing air in at the same rate it's taking air out I'd guess the majority will stay within the system

Before you bother with anything I would suggest you should have very good insulation and possibly double glazing, depending on the aim of your system. If you just blow a bunch of cold air into a warm house you'll just push the warm air out.

We have a cheap ventilation system at home, installed before I bought the house. I have it on a cheap digital mains timer so in summer it blows air in when it's cooler outside, and in winter it goes when it's relatively warm outside. For example in winter it's on 11am - 3pm and then for a few 15 minute bursts in the evening. It doesn't need to be on 24/7, we only have three people in our house and we extractors in the kitchen / bathroom.

Kickinbac

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#1716462 7-Feb-2017 12:22

The hardest problem DIY is the controls as it should switch the fan on/off based on the temp in the roof space and temp in the house. Theres no point blowing cold air into your house in winter or hot air in summer. A controller could be built with a arduino or simliar.

You can buy Smartvent kits from electrical wholesalers, they include all the bits you need including the tape and fairly straight forward for the average DIYer to install. Probably cost about $1500.

Kickinbac

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#1716468 7-Feb-2017 12:38

Also other things not in your list that you will need are Y-branches and/or branch takeoffs (say $60 each) and you need one for each grille, a fan (say $200 - $400), a filter box for the filter.

Once you add all these bits up the price, simplicity and included controls of the smartvent kits don't look so bad.

For these bits and pieces try smooth-air.co.nz but not sure if they sell to the general public. They also do kits.

An inline electric duct heater costs between $600 - $1000 depending on size and can come prewired with a thermostat in the air stream. You'd need a sparky to wire this all up.

I'm not going to get into the debate on postive pressure vs balanced heat recovery systems as there is plenty of info on the geekzone forums.

timmmay

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#1716477 7-Feb-2017 13:00

I don't like ventilation systems that take air from the roof space. Ours did, but it's an old house and it smelled. I extended the ducting and now take air from the eaves. It can help heat the house in winter, but in summer it means your ventilation system can't really run during the day.

MikeAqua

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#1716513 7-Feb-2017 13:51

We put a HRV system (smart vent, air to air heat exchanger) in a 1950s house that was far from air tight - older wooden windows etc.

It still worked well and reduced our power bill by drying the house out and increasing the apparent warmth at a given temperature. We turned the heat pump down a couple of degrees for the same comfort level.

Mike

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Starina

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#1716588 7-Feb-2017 15:02

Thank you for your responces.

timmmay:
Before we can offer much advice you should tell us why you want a ventilation system, what problem you're trying to solve.

Get rid of crying windows (single glazing), mold in the rooms facing south, mold on the curtains, stale air (behind beds, bookshelves, etc). Reduce moisture in the house to be able to heat/cool it more efficiently

timmmay:
The 2kw inline heater will just be heating a wire with power, far less efficient than using a heat pump 2kw won't go far for a decent sized house
Generating heat in one place and sending it to each room will lose a lot of heat, even using insulated ducting.

I know about it. However, heat pump heats the air just a bit (not like from 4 to 20), and air has to pass it several times to reach the desired temperature. In case of inline heater the air is heated from any temperature to any temperature for a just one pass. I am aware that it's not as efficient as heat pump, but I don't want to throw cold air in the house during the winter. It will be turned on only in winter nights to make the air move.
Heater (ex: Moisture master) has several levels of heating, and the second one gives more than 10 degrees increase consuming less than 1kW.
Do you think that insulated ducting will loose heat even if I wrap it with earthwool? I thouhgt it will help with the heat transfer issue.

timmmay:
I'm not sure a sealed house is a requirement for a heat recovery system. Sure if it was sealed it might work a little better, but if it's blowing air in at the same rate it's taking air out I'd guess the majority will stay within the system
Before you bother with anything I would suggest you should have very good insulation and possibly double glazing, depending on the aim of your system. If you just blow a bunch of cold air into a warm house you'll just push the warm air out.

As far as I found our, sealed house is almost a requirenment. It works much better as the is no way for the cold moisture air to get in. We have a cat door, lots of small holes in french doors (for the water to leave). So, I don't think that this is called airtight (however, it was built in 1990). It depends on the definition of 'airtight'. I think that our house is not.
Moreover, heat exchanger costs much more. The smallest quote I have is for $6k.

And, what is important, I think that it's easy to convert positive pressure system into 'ballanced'. A heat exchange thing, few more vents will be needed and some rerouting with the incoming flow. I am planning to install vents in places where I will be able to reuse them in ballanced system just in case.

Double glazing starts from $20k. Way too expensive. Under the house and ceiling insulation will be added after I deal with the ventilation system.

timmmay:
I don't like ventilation systems that take air from the roof space. Ours did, but it's an old house and it smelled. I extended the ducting and now take air from the eaves. It can help heat the house in winter, but in summer it means your ventilation system can't really run during the day.

I was in the roof space. It's hot and I didn't noticed any smell. So, should be fine.
A simple fan that I mentioned earlier, that will suck the air FROM the house, Y-branch with valve can help. Turn the main system off, turn the switch, it will switch the Y-branch and use existing vents to get the air out of the house. It will make a breeze. New air from the outside is a bit colder that in the heated house.

Kickinbac:
For these bits and pieces try smooth-air.co.nz but not sure if they sell to the general public. They also do kits.
An inline electric duct heater costs between $600 - $1000 depending on size and can come prewired with a thermostat in the air stream. You'd need a sparky to wire this all up.

Thank you, I called them and they confirmed that general public can buy anything that is on the website (excluding things made by a special order)

Summary so far:
A simple system with incoming airflow at one speed could be enough.
If I add costs for control panel, branches, than it's possible that DIY SmartVent can be cheaper (in Bunnings SmartVent Ventilation System 4-Outlet costs $1665) without an inline heater.

timmmay

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#1716630 7-Feb-2017 16:20

Ah yes, ventilation should help with mold. Interesting that you say heat pumps only heat the air a little, the output temperature of a heat pump is around 50c or higher, from the time it turns on, but this has to heat all the air and objects in the room. The inline heater will be less effective, raising air temperature a similar amount and cost more to run.

A 10c increase in temperature in the main line of the ventilation takes the air from say 0 to 10 degrees, which I guess is some help. However if you run the fan speed low and use a heat pump I don't think it'll matter all that much. Like I said above I keep ours off on really cold nights, in winter it runs mostly during the day with just the odd on time after cooking and at the end of the evening. On nice days we open the windows - the PVC double glazed we just got lock open nicely.

Insulating over the insulated ducts should help it at least a little, I would guess.

Placement of air vents is a bit different between positive pressure and balanced. With balanced you draw the air across a room, with positive pressure I think you just put them where convenient that won't make a draft, but you could reuse them. If you have heat recovery ventilation you can deliberately extract air from a bathroom in order to reclaim more waste heat, but that's not ideal in summer. If you move to balanced later I suspect unless it's DIY the cost won't be much less than doing it up front, unless you find a good company.

Double glazing with PVC (ie high quality) cost me $13K and I did the painting myself, that's for an average sized family home. It is expensive.

All in all your idea of a fan and some ducting seems reasonable, and taking air from the roof space seems fine if it's clean and warm. Just don't run it during the day in summer or your house will get pretty hot.

Starina

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#1716652 7-Feb-2017 16:39

timmmay:

Interesting that you say heat pumps only heat the air a little, the output temperature of a heat pump is around 50c or higher, from the time it turns on, but this has to heat all the air and objects in the room. The inline heater will be less effective, raising air temperature a similar amount and cost more to run.

A 10c increase in temperature in the main line of the ventilation takes the air from say 0 to 10 degrees, which I guess is some help. However if you run the fan speed low and use a heat pump I don't think it'll matter all that much.

Sorry, I read about it a long time ago and recently some heatpupm guy said the same. That is why I was so sure about it, but I'll check it.
Basically, everything it can do is to heat existing air for a few degrees (it can't get you 30C at once if the room temperature is 10C), and it reaches the desired temperature only because it constantly increases the air temperature (don't know the numbers, for example from 10 to 15, then existing slightly cooled from 13 to 18 and stops if the desired temperature is reached.) That is why you can't add much cold air from the outside (I heard the number not more than 5%). It just won't be able to heat or cool it. Otherwise ducted heatpump could take the air outside and work as a positive pressire ventilation system even in the heating mode. But it can't.

My quote for retrofit glazing (with existing aluminium frames) was $20k.

Sure, conversion from positive pressure into balanced only in case of DIY.

timmmay

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#1716708 7-Feb-2017 18:21

All heaters work by increasing the temperature a bit at a time. Air going into a heat pump at 10 - 15 degrees comes out around 50 degrees, as measured by both the heat pump service guy and my IR thermometer. A heat pump definitely doesn't just increase the air temperature by a few degrees, it's a really big 30 degree or more jump. I think what you've been told is false. Get an IR thermometer and try it yourself. I have a heat pump as my only source of heat all winter, the house is warm and comfortable, though heat pumps can be a bit noisy.

Once it's in the room, heat is heat. Most heat the air directly, those ones that go red heat the air a little but heat objects a lot, but those objects then heat the air. Those wall radiators that they have in the UK are much the same, they heat the air up to maybe 50 degrees (more?) which moves around the room with air currents, but they're nice and quiet. Basically all heaters are fairly similar, fan heaters and heat pumps do much the same job in very different ways, but heat pumps are far more efficient.

TLDR: heat pumps provide great heat, economically, you've been given misinformation, do some reading.

Hammerer

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#1716722 7-Feb-2017 18:32

I notice that timmay has replied while I was typing this so there will be some repitition

Personally, my priorities for a ventilation system would be:

1. Have a controller that maximises "free" warm air in at winter and "free" cool air in at summer. Not the opposite.

2. Have lots of insulation because it most likely has the best payback.

Inline heating can lose a lot of heat through the ducting which has a high ratio of surface area to the volume. That's why you definitely want to add as much insulation as you can when ducting air with a temperature difference. A rough rule of thumb that I've used is that R11-15 insulation will at least halve the heat loss assuming the ducting is not leaking.

There are quite a few online calculators to help you with the scenarios, e.g. http://www.remak.eu/en/thermal-insulation-and-ductwork-heat-loss-calculation

3. Have a ventilation system with a heat exchanger for the entire house unless you won't be there long enough to get payback or the house is tiny with little scope for large enough annual savings.

4. Use heat pumps for all other heating.

I'm not sure why you're so anti heat pumps:

Heat pumps can be four times as efficient as a radiant system.
I would be more likely to use a heat pump because a well-designed ventilation system can improve the efficiency of household heating by assisting the transfer of heat throughout a house. Without the pressure from the ventilation system warm ari doesn't tend to move between rooms.
An effective heating and ventilation control system can half the cost of operating by doing many of the things already mentioned: bringing in winter air when it is warmest, bringing in summer air when it is coolest, ensuring that the heat pump is operating optimally i.e. with a smaller temperature differential, keeping consistent and relatively low air speeds in the ducts to reduce turbulence which increases heat transfer/losses, etc.

Starina:

Basically, everything it can do is to heat existing air for a few degrees (it can't get you 30C at once if the room temperature is 10C), and it reaches the desired temperature only because it constantly increases the air temperature (don't know the numbers, for example from 10 to 15, then existing slightly cooled from 13 to 18 and stops if the desired temperature is reached.) That is why you can't add much cold air from the outside (I heard the number not more than 5%). It just won't be able to heat or cool it. Otherwise ducted heatpump could take the air outside and work as a positive pressire ventilation system even in the heating mode. But it can't.

It's kind-of true what you were told but you are misinterpreting its significance. You are describing the heat transfer from the heater to the air. A hot radiant heater can heat air that does not touch it whereas a heat pump mainly transfers heat by airflow over its coils - just like a heat exchanger. So for the same airflow an inline ducted radiant heater may be capable of transfering thermal energy to the air more quickly than an inline ducted heat pump. That means it probably won't need as much air to provide the same amount of heat to the house. Which is why, if all the air that is being heated comes from outside then a positive pressure system could be pushing more of it out with a heat pump leading to the worst case scenario you describe.

But that is the wrong question to be asking. You should primarily be interested in the overall transfer of heat to air in the house. In general, if you have use 2kW of electricity in a radiant heater then you get 2KW of heat but a heat pump can product up to 8kW from that 2kW of electricity. The heat pump might have to (re-)circulate more air to transfer the same amount of energy to the air but it has more heat to give. So the heat pump will heat it up your house much more at the same cost.

In the real world a wasteful situation where an in-line heat pump is forcing more heated air out of the house would not be tolerated. A well designed in-line ducted heating system would use features like recirculation of internal air so no more heat is lost from the house than would be with radiant inline heating. In this case, the higher cost of heat pumps and heat exchangers would be recouped through higher operating efficiency.

P.S. Here are some topics that have more information which may be useful to you. There are lots of others too:

HRV installation help

Positive Pressure or Balanced Pressure ventilation system?

Ventilation system paired with heat pump/heat transfer system?

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#1716723 7-Feb-2017 18:34

Have you thought about buying a 3 room heat trans pro series? You can get one for around 580ish then convert to home vent system

mclean

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#1717133 8-Feb-2017 11:37

Some points:

You need to distinguish between heating systems and ventilation systems.

If your problem is moisture control in the house then you need a ventilation system which feeds dry air into your living spaces. The volume of air you need to do this successfully depends on how dry the ventilation air is and how many people there are in the house. There are rules of thumb for this: 0.5 air changes per hour should be more than enough, and in most cases you can go down to 0.35 air changes per hour (which is what the NZ Standard requires). When you work it out this is a VERY SMALL volume of air. Unless you are smokers or particularly smelly, in which case you might want to increase the ventilation volume for odour control.

Heating the ventilation air doesn't change its moisture content and does nothing the improve the effectiveness of the ventilation. The only reasons you might want to heat it are to manage condensation on ducts running through moist roof spaces, or to avoid cold draughts when you introduce the air into the rooms. Heating the air to about 15 degC is usually good enough for this. (In the HVAC trade this is called "tempering" rather then "heating" because it doesn't really contribute to the space heating.). To do this properly you need a constant supply air temperature controller, but there are simpler ways. Using these principles the amount of heat you need is very small - never enough to justify the complication of heat recovery.

You need the ventilation air to be a dry as possible. In winter this always this means using outside air. Don't fall into the trap of thinking that cold winter air has more moisture in it - the opposite is true.

Understand that I am just talking about ventilation for moisture control here. If you want your ventilation system to heat or cool your house that's a whole different story.

Starina

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#1720031 14-Feb-2017 14:13

Thank you for your replies.

Took me a while to understand what I want and do and check the options.

timmmay:

All heaters work by increasing the temperature a bit at a time. Air going into a heat pump at 10 - 15 degrees comes out around 50 degrees, as measured by both the heat pump service guy and my IR thermometer. A heat pump definitely doesn't just increase the air temperature by a few degrees, it's a really big 30 degree or more jump. I think what you've been told is false. Get an IR thermometer and try it yourself. I have a heat pump as my only source of heat all winter, the house is warm and comfortable, though heat pumps can be a bit noisy.

Thank for the info. I'll check it with my heat pump. Probably it needs some maintenance.

Hammerer:

Have a controller that maximises "free" warm air in at winter and "free" cool air in at summer. Not the opposite.
Have lots of insulation because it most likely has the best payback.
Have a ventilation system with a heat exchanger for the entire house unless you won't be there long enough to get payback or the house is tiny with little scope for large enough annual savings.
Use heat pumps for all other heating.

Agree with this. A positive pressure with the 'summer kit' or a balanced system with the 'summer bypass' can cool the house after a sunset.

Insulation will be added on top of the existing after I deal with the ventilation.

Hammerer:

I'm not sure why you're so anti heat pumps:

I am not. I love them! :) With 2kW electricity consumption they produce up to 7kW of heat or 6kW of cold. It's very efficient.

We have one heatpump in the living area, but it can't help with the moisture/mold/crying windows. That is why I am looking into ventilation to get rid of the moisture.

The cheapest option I found so far is a ventilation system Dry-Matic from smooth-air. The price is $2,645 for the system with digital controller and a 1.5kW heater. Plus around $350-400 for ducting, fittings, grilles.

The heat exchange model starts from $4k ($1k more expensive). For our house it's much more difficult to install it as there are no soffits, so I need to make a hole in the wall and be sure that it's properly sealed. The second thing is that the manhole to the attic is also small and it will be difficult to bring a heat exchange unit there.

So, for now I think that I will install a positive pressure Dry-Matic with a heater (to be able to run it in the winter, not to heat the house). Then I'll add insulation for the ceiling and under the floor.

My existing heatpump will be used as a heat source as well as eco panels. I hope that with the reduced moisture they will be more efficient.

Does anyone know about the protocol which Dry-Matic uses to communicate with the unit? Is there any way to connect an Arduino/ESP8266 to be able to control it from the outside?

Thanks.

timmmay

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#1720069 14-Feb-2017 15:27

I'd not bother with the heater in a ventilation system, mine has one and I never use it. Just use your heat pump.

Eco panels are only eco because they use a small wattage, they put out 1 watt of heat for every watt of power.

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