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  1. Sometimes questions are raised as to whether it's worth increasing insulation levels and often there seems to be confusion as to what the "ideal" level of insulation is, or even what a "good" or "reasonable" level of insulation might be. I'm not sure whether or not the non-linear impact of improving insulation, in terms of the effect on the heating requirement, and hence running cost during cold weather, is widely understood. I've heard comments like "it's not worth improving the insulation from 0.16 W/m2.K to 0.12 W/m2.K because it would be 30% more expensive and only reduce the heat loss by 25%". Most of the time this is incorrect, because homes have heat sources all year around, from the occupants, incidental heating from appliances, solar gain and even pets (a medium sized dog is probably a four-legged 40 - 50W heater). So, I thought a really simple example might help some gain a better understanding of this non-linearity, and illustrate better why some are so evangelical about trying to improve insulation levels (and reduce ventilation heat loss, too, but I'll get to that another time). Let's build a pretend house, that for simplicity has no doors or windows and is a rectangular single storey box with a flat roof. For simplicity we'll assume it's on raised piles, with an air space underneath, just so we can use the same insulation level on all six sides and to make the sums simple. All I'm doing here is making a comparison, so this is a valid way of illustrating this effect. In our rectangular box house we have an average of 100W of incidental heating, coming from things like internet kit, a PC, a cordless phone base station, a TV, a phone charger, a few lights and a handful of intermittently used kitchen appliances. This is a pretty low figure - I struggle to keep our house background load below about 200W, without any lights on. The box houses two adults, giving out around 80 - 100W each and a dog, so lets say there is 220 W of heating coming from the occupants. The box also has a heating system that can deliver whatever power is needed to maintain a temperature of 20 deg C inside, and its night time, so there's no solar heating of the walls. Outside it's 5 deg C, a chilly winters night. This rectangular box is 10m long x 10m wide x 2.5m high inside, so has a total wall, floor and roof area of 300m2 and an internal floor area of 100m2, so fairly average in size (a bit bigger than our current 3 bed bungalow). So, we have a temperature difference between the inside and outside of 15 deg C (20 deg C - 5 deg C), an internal surface area of 300m2 and a constant incidental heating level of 320 W (220 W from two adults and dog, 100 W from electrical appliances and lights). First, lets see how much heat we need to put into this box from the heating system, if we have U values for the walls, floor and roof of 0.2 W/m2.K (K is degrees Kelvin, the same units as degrees Centigrade when only temperature difference is being compared): The total heat loss power, in Watts, can be calculated from the U value, the area and the temperature difference, so for this first example we get 300m2 area x 15 deg C temperature difference x 0.2 W/m2.K U value = 900 W. There is 320 W of heat coming from the occupants etc, so the heating system would need to deliver 900 - 320 = 580 W in order to keep the house at 20 deg C under these conditions. If this were by direct electric heating, then the heating cost would be about £2.09 per 24 hours. Next, let's see how much heat we need to put into this box from the heating system, if we have U values for the walls, floor and roof of 0.1 W/m2.K , in other words, we've made the insulation twice as "good", so might think we've halved the heating cost: The total heat loss power is now 300m2 x 15 deg C temperature difference x 0.1 W/m2.K U value = 450 W. This is what we'd expect, double the insulation effectiveness and halve the heat loss. However, when we now take away the incidental heat gain from the occupants, etc, of 320 W, the heating system needs to deliver 450 - 320 = 130 W in order to keep the house at 20 deg C under these conditions. If this were by direct electric heating, then the cost would be about £0.47 per 24 hours. So, by doubling the insulation level we've decreased the heating cost by about 78%, not the 50% that might have been expected. This is a very simplistic example, but it does illustrate why doubling up in insulation can give a far greater benefit than might be expected. It also shows why, when you improve the level of insulation you can reduce the heating requirement down to such a low level that for a lot of the time you don't need any heating. In that last example, turning on a few extra lights could heat this imaginary box home to a comfortable temperature on a cold night, whereas with only half the insulation it needs something that delivers 446% more heat.
  2. Hi, Has anyone installed a heat recovery unit for the shower / wet room? Just wondered if it's worth the effort / risk of failure vs marginal waste heat recovery? I was looking at the Passive House component database and they had a section on it, this one caught my eye as it was the best performing (just listed as an example only): http://www.showersave.com/qb1-range/ I might look at including something similar in my build, a horizontal one for the wet room and the vertical one for the ensuite shower. Just curious what people's thoughts are on these generally?
  3. Hi All - i think the filters on my mvhr unit need changing. I’ve just read the manual and it says they should be replaced every 12 months but I’ve only been in my new home 5 months and the machine sounds like it’s having to work quite hard. It’s gotten much noisier. My sustem is Vent Axia Lo Carbon Sentinel Kinetic V MVHR system. I tried to hoover the current filters this evening but it’s a really tough task with little success. Does anyone one know where I can buy replacement filters from for cheap?! I’ve looked online and they all seem really pricey. If you have to change them regularly then it’s really going to add up! Any advice would be really helpful. Also, I’ve seen online that there’s different grades of filter quality. Can you really tell the difference? Thanks
  4. Hi, I have installed a Villavent mhvr system in my new build a few years back and it’s been running fine. I never got my final ticket, due to a lack of funds and had to just move in. I now desperately need my final ticket , so I can try to claim vat back. Do any of you clever people know the cheapest, easiest way for me to get a commissioning certificate passed on my system for building control. Im in Conwy, N.Wales. Appreciate and look forward to any help. Thanks Paul
  5. Hi. I am a home ventilation specialist and work for BPC ventilation that are leading designers and suppliers of home ventilation and heat recovery systems to builders and self builders throughout The UK, Ireland and most other worldwide locations I will try to answer any questions and explain the facts from the myths Gary