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I see little use in "3D" for the detail design, accept maybe where there are non-standard details/junctions that would benefit from teasing out the issues before it comes together on site. A 2D drafting package should therefore be fine for producing the Building Control drawings and all plans and layouts that the onsite trades will use. An Architectural package will have workstreams optimised for producing such drawings so should save time. Their capabilities are all rather similar so take your pick. For the concept design phase I found a huge benefit in using a 3D application, to get proportions, scale, flow and material selection all the best it could be. I can't see it matters whether that's a virtual 3D CAD model or a physical 3D model, as long as it's a medium that's relatively quick to change and trial different options. The important bit is that is fleshes out any awkward junctions and make you think about how the structure will come together. I used the CAD and visualisation packages I was already familiar with for doing this as the "best" CAD package is the one you already know. However if I didn't have that existing knowledge I'd have used SketchUp. It's free, quick, and very flexible for applying materials and textures for reasonable quality renderings.

Essentially it's just a normal MVHR unit with a reversible air-to-air heat pump built in, so it can add around 1.5 kW of heat to the fresh air distributed around the house or remove around the same amount of heat by pumping cool air into the fresh air distributed around the house. The main advantage is that it's a "single box" solution, that is installed in exactly the same way as an MVHR unit, with no additional ducting, plumbing or wiring connections. The main disadvantage is that it is really just a comfort cooling unit, or heating for a house with a low heating demand (it would happily keep our house warm in winter on it's own), and isn;t well suited to use in houses that are less well insulated or airtight.

Didn't work: 1. Complicated heating controls, after many months of playing with weather compensation, controlling the house temperature using the floor slab temperature and assuming that the logical link between floor temperature and house temperature would work well at controlling the latter using the former, I realised that, as the heating system only provides a small part of the total house heating, it would never work, so I gave up and installed a very simple room thermostat, which works very well. Should have done this in the first place. 2. Water filled thermal store. No matter how much extra insulation I added around it, the heat losses from it were still very high, over 2 kWh per day (as supplied, with a double layer of insulation, the losses were over 3 kWh/day). This cause the services room to get up to around 40 deg C in summer, damaged the oak door between it and the bedroom and caused the adjacent bedroom to badly over heat. Swapping the thermal store for a Sunamp PV, with it's massively lower heat losses, completely fixed the problem, and freed up lots of room in the services area, too. 3. Complicated ozone injection and flow rate control system on the borehole feed. It worked, but was far too complex and has now been replaced with a much easier to service, very simple eductor, that is far more effective at adding and mixing ozone to the incoming supply and also easier to service and repair. The brass eductor took two goes to get right, but has no parts to wear out, no flexible seals and should last forever. Did work: 1. Choosing an insulation system with a high decrement delay factor. Not only does it significantly improve the comfort level in the house, by helping to keep the internal temperature steady, but it has the added bonus of being an extremely good acoustic insulating material too, so improves the soundproofing and deadens the internal acoustics a fair bit (handy in a house with a lot of hard surfaces). 2. Opting to have UFH inside the insulated concrete slab. This forms a nice big "storage heater", yet responds pretty quickly when needed. Having a heated (or cooled) power floated slab that was flat and smooth enough to lay flooring to directly saved a lot of hassle and money. 3. Choosing the more expensive Genvex MVHR with the internal air-to-air heat pump. It's not massively effective, but does do a pretty good job at keeping the bedrooms a degree or two cooler than downstairs in very hot weather. It also does a great job of drying out towels or washing left on the drying rack in the utility room. 4. Avoiding the use of highly paid consultants etc whenever possible. I found that, with a bit of effort, I didn't need to use many at all. It seems that when you are self-building a house every Tom, Dick and Harry comes at you with their hand held out for more of your hard-earned cash - you can avoid paying out a lot of this with a bit of determination and time.