Ventilation System Engineer/Installer

We live in an apartment with no ventilation and a Demand Controlled Ventilation system was proposed by Aereco as a good ventilation solution. Unfortunately the Aereco solution was rejected by our management company as they don’t allow any units or ducting within the loft areas.

We’re now looking at a cheaper and more basic solution which involves installing two Vent-Axia Lo-Carbon NBR dMEVe HT extractor fans 474497A (kitchen and bathroom) and the three Aereco EHt 969 Wall Humidity Sensitive air inlets originally specified for the living room, bedroom and office.

Our problem is that we don’t know for sure that this is a good solution. Can anyone recommend an installer who does have sufficient ventilation system knowledge to check out our revised option and put together a new proposal for the management company?

Perhaps someone can put forward a better solution? I would add that our heating bill is pretty low and I don’t think that for us, heat recovery units are a viable option.,test%20method%20and%20listed%20on%20the%20PCDB%20database.

I’ll be interested in the reponses, we have been advisef to get Mechanical extract ventilation as we don’t have any extract in the kitchen or bathroom. Worried about bringing cold air in, and cost, I wondered if single mechanical heat recovery units in bathroom amd kitchen would work, or some people use paired units? but don’t really know wherr to go for advice. We live in cumbria and have also been advised to do a radon test…which might have an impact.

If you live above igneous or metamorphic rock you have a higher risk if radon. Research carried out by the Passivhaus Institute in Germany found that an effective way of almost eliminating radon was continuous whole house mechanical ventilation. I suggest that you consider a linked set of single room MVHR units or a whole house ducted MVHR. Continuous ventilation without heat recovery will lead to either a cold house or a huge energy bill, and maybe both.

I suggest you contact a company such as the Green Building Store to discuss the options.

Get one with a humidistat and back draft stop in the bathroom asap, any electrician will do this. Setting it up with the correct time delay and humidity is a bit fiddly but worth the fine tuning - get them to explain what you need to do, as they won’t have time to get it right. When correct, you won’t need to keep the window open.

You can control humidity in the kitchen with a large cooker hood that vents outdoors. There are a number of things you can do to help reduce moisture.

Heat recovery for the bathroom only isn’t really worth it.

A full mechanical ventilation system is a large undertaking.

That depends on your preferred temperature, heating method and amount of time the bathroom is in use. By “in use” I am including use as a drying room. The hotter you want it, the more expensive your heating and the longer it is in use the more worthwhile heat recovery becomes.

I have just reread the original post to reacquaint myself with the problem. Whole apartment heat recovery without loft access is possible but as @Frank_Reif says it is a big undertaking and without loft access will impact the living area; mainly aesthetically but also regarding wall space.

As a general rule I still recommend whole property MVHR as part of a larger retrofit project but I don’t think I can in your case.

They’re expensive, noisy and not very efficient. The ones I found are often designed for very high use rooms, like sports centre changing rooms. Individual room heat recovery is only worthwhile when ventilating large volumes.

The shower is the key source of moisture. You can’t do much about reducing how much they generate during the shower, but it’s a good idea to wipe off the water off the glass/tiles/tray and get it down the drain, rather than wait for it to evaporate.

The Americans have a long history of dealing with the consequences on running ventilation through unconditioned attics. There’s a lot that can go wrong.

At the moment, spray foam to create warm roof, then installing the ventilation, is the most cost effective retrofit solution. Unfortunately, because I hate the material.

The best opportunity to do it well is when fixing the roof.

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I have no personal experience of single room MVHR but a nephew swears by his.

Absolutely. No shower is complete without a squijy blade. (I have no idea what the correct spelling of “squijy” might be!:frowning:)

At least the OP now has both sides of the argument and can make an informed choice.

It isn’t an amateur job to fix ducting in a loft, conditioned or not, warm roof or not. Two other issues are heat loss from the ducts (mine are insulated, even though in a warm roof) and air transfer into the loft from poorly sealed penetrations of the ceiling/vapour control barrier.

Having said that an informed and motivated amateur could possibly do better than some professionals.

In conditioned attics, you only need to insulate them for AC and with ducted heating. Otherwise, a bit of leakiness isn’t that bad, because it represents air changes in the attic space, which manages moisture.

I like recirculation systems, which ideally need metal ducts and low static routing/fittings. That’s more difficult to do well.

Can you elaborate a little, Frank, for us beginners? These are terms I haven’t come across before.

This was a good presentation:

Ventilation needs a nice smooth route to flow through the duct system. Otherwise it becomes unreliable and noisy.

Recirculation involves 3-10 times more airflow than for fresh air alone.

Americans have ducted heating systems, which are well suited to heat pump, and somewhat for redistributing solar gain to the shaded side of the building. It’s also used for AC (sensible cooling, not dehumidification) for the same reason.

By putting a heat exchanger in the way of that airflow, you get a lot of heating/cooling power using lower grade heat (heat close to room temperature) which is cheaper to produce and easier to store.

The issue of course is that the ducts become considerably bigger, and then how do you find a path through the building, especially in retrofits?

Vertical floor to floor distribution is easy, much like the soil stack, but horizontal distribution is often the hardest.

Using attic space and between joists in intermediate floors is often the only way to do it. However, every additional bend in the system, increases the pressure required to move that air.

It takes a serious bit of planning to get it right.

The extra storage and mechanical space you get from conditioning your attic with an over rafter insulation system is worth it in my opinion. This also allows for a good continuous thermal layer to your EWI whilst maintaining the same, or greater, overhangs.

Many thanks, @Frank_Reif. That explains it brilliantly. I have often read Allison’s obviously authoritative contributions on the U.S. Green Building Magazine blog, but haven’t always understood all of them, whereas this video is pretty comprehensible.
I am determined that if a local builder has the skills, and I can find a plot, my self-build, timber-frame passivehouse will have air-to-air for heating and cooling (but won’t need a lot, I hope). ‘Ductless mini-splits’ seem to be all the rage for new-build in that magazine’s blogs.

Yes I gather the way to retrofit this is to take a chain saw to the parts of your rafters that project beyond the existing outside wall surface. Retrofit is so much more complex and expensive than new build! And stepwise retrofit such as we might continue to contemplate for our house, if we stay instead of building new, needs serious commitment! But someone is going to have to pay for and undertake the retrofitting of each of our leaky, drafty, UK dwellings. Your and Tim Gilbert’s expert contributions to this forum are hugely appreciated, as well as everyone else’s, in this respect. Many thanks.

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Very kind of you to say that.

Although, I wouldn’t consider myself an expert. The true skill comes down to project management and sequencing to maximize labour efficiency.

The community organising going on here is by far the most challenging thing to get right, because it will allow multifamily outfitting of several adjacent buildings/units to be possible.

I just want to get some of the simpler, more objective, stuff out of the way.

I hope to live in a car free neighbourhood, in a mid rise point access passive house apartment block, with a modest amount of space per person but very good public facilities. I can see the appeal of detached rural living, if it weren’t for the complete lack of young people I’d consider it! Each to their own.

A ducted heating system can now easily accommodate heat distribution with refrigerant.

However, I don’t like mini splits, because of their complexity and greater risk of poor commissioning and refrigerant leaks. I’m not sure why there’s such a fad at the moment.

I would instead stick with co2 monoblock heat pumps in rural settings, as it allows for large quantities of thermal storage to be added. Co2 operates close to Carnot efficiencies across 90deg C deltas. Larger multifamily heat pumps at the +100kw scale become even more efficient.

Preferably from a water source, or modest ground source. <35degree C design temps with hydronic distribution and convector rads would be ideal.

The simple truth is that we should be designing all of our buildings to have sufficient thermal storage to use the cheapest 1/6th of grid electricity in a 24-100hr period. The more remote the more individual storage you need.

Low temperature heat network sourced heat pumps in cities will provide incredibly cheap heat due to district scale seasonal TES.

So if you insist on your rural setting, then include 100hrs TES, and plan for it taking up 1.5m3/100kwh.

There’s lots of historical precedent to change building layouts to accommodate new heating systems. It’s just we have been pitifully slow to recognise the need to do this. I have yet to find a prominent figure pushing for this I’m afraid.

Totally off topic, but there you have it.

Remember that not all rural inhabitants have a choice in the matter, but I do agree that high density housing provides more opportunities for energy efficiency, whether for form factor, heating, transport or the removal of any need for transport.

Having been let down several times by contractors saying they would fit an A2W heat pump to replace my boiler (current flow temperature 45°C) I am thinking of fitting a mini/multi split A2A to share the house’s thermal load, hopefully covering the full heat requirement in the shoulder periods. I will then be able to get by with a much smaller A2W. I would then have both the advantages and disadvantages of both systems but more importantly I would not be totally dependent on one system.

The question remains about how to control this combination.