Alslo Posted February 7, 2020 Share Posted February 7, 2020 Hi I would be grateful for your thoughts and expertise regarding correctly sizing the air to water heat pump for our new self build home. I have inputted our spec into a few companies own calculators that came back with different results. I fully expected this as our house didn't really fit into the criteria being asked for on there calculators. I will give you all the details I can think of. The floor area is 170 square metres. Its one and a half storey. Wall construction is Canadian log style pine timber with sheeps wool and rubber seal joints. The diameter of the logs is between 40 cms and 70cms. 30 cm sub floor with DPC membrane, followed by 5 cm high density kingspan insulation foil backed, underfloor heating in 10 cms screed/stone mix finished polished. Triple glazed windows and doors. Roof construction consists of 2cm timber finish board, followed by breathable membrane with 10cm high density Kingspan insulation foil backed,then 5 cm air pocket followed by breathable membrane followed by 5cm air pocket finished with fired tile. Downstairs the house is open plan with a central fireplace housing two flues for a solid fuel stove and a solid fuel range cooker. One will be lit most of the winter cold days. There are four rads upstairs. Plumbing will be two showers and one bath. Two bedroom with two inhabitants. The house location is Slovenia where the average ambient temperature during the winter is between 3 and 5 degrees below the UK if this helps? I look forward to your help. Regards Al. Link to comment Share on other sites More sharing options...
SteamyTea Posted February 7, 2020 Share Posted February 7, 2020 Do you know the thermal properties for each component that is exposed to the outside? Then it is a case of hunting around on here to find @Jeremy Harris's heat loss spreadsheet, punting in the numbers and seeing what comes out. Link to comment Share on other sites More sharing options...
Alslo Posted February 7, 2020 Author Share Posted February 7, 2020 Cheers steamy tea. Hopefully Mr JH will see my post. From what I see on here, he knows his stuff as do a lot of you guys. Thanks for your time. Link to comment Share on other sites More sharing options...
SteamyTea Posted February 7, 2020 Share Posted February 7, 2020 Can you get hold of decent weather data in Slovenia? Our Met Office is pretty good, but there is a large amateur network, WeatherUnderground, that has thousands of weather stations in most countries. Always worth a look to see what is near to you. The calculations of heat loss are fairly basic. This site is a mine of knowledge: https://www.engineeringtoolbox.com/heat-loss-buildings-d_113.html Link to comment Share on other sites More sharing options...
joth Posted February 7, 2020 Share Posted February 7, 2020 Link to comment Share on other sites More sharing options...
Alslo Posted February 7, 2020 Author Share Posted February 7, 2020 Thanks for your help guys. I will check out the local weather data. I will also look at the chart although my brains are in my hands and not upstairs. Cheers. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 7, 2020 Share Posted February 7, 2020 @Alslo, I've just updated the spreadsheet link in that old post that @joth linked to, as back when I posted that the forum wouldn't accept spreadsheet files and now it does. Hopefully the spreadsheet should be fairly easy to work through, the hardest part might be getting local temperature data for your location. Link to comment Share on other sites More sharing options...
Alslo Posted February 7, 2020 Author Share Posted February 7, 2020 Thanks Jeremy. Infact I was just checking our weather here. I was surprised for such a small country, we are discribed as having four climates. We are in the south west and so we are classed as being oceanic. Looking at the data shows average summers 26 degress, winter is zero but during our experience here it's getting warmer and shorter. I will have a look at your spreadsheet. Please dont be surprised when I get back to you for advice. As I said earlier there's not to much upstairs. Thanks Al. Link to comment Share on other sites More sharing options...
Alslo Posted February 7, 2020 Author Share Posted February 7, 2020 Hi, I have been looking through the spreadsheet entering our data. There are a few areas I had to leave as they where as I pretty much don't get it, sorry! When you come to the end I was expecting a enter button. What am I doing wrong? Link to comment Share on other sites More sharing options...
SteamyTea Posted February 8, 2020 Share Posted February 8, 2020 13 hours ago, Alslo said: expecting a enter button. What am I doing wrong? Probably nothing you are doing wrong. Try pressing F9, that recalculates a spreadsheet if it does not do it automatically as you enter data. You may find that some cells need data, so which ones where you unable to fill in? Link to comment Share on other sites More sharing options...
Alslo Posted February 9, 2020 Author Share Posted February 9, 2020 Morning. I'm having a problem finding the u value of the average diameter of my logs. From what I have looked at on the net, most are US sites so are valued in inches, that's no problem converting into metric. They are saying U value for softwood is 1" =0.64, my log diameter average is 15". So 15 x 0.64=9.6. Now I believe for the calculator I need to change this figure into W/m2.k? If so this is a conversion according to google of multiply by 5.678 = 54.5088. This figure doesn't look similar to the one in the spreadsheet. ??? Link to comment Share on other sites More sharing options...
SteamyTea Posted February 9, 2020 Share Posted February 9, 2020 Try using 0.25 m.K/W See if that gives a sensible answer. (What Wikipedia quotes as the RSI value for most timber) Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 9, 2020 Share Posted February 9, 2020 Depends very much on the moisture content, I believe. I used a value of 0.15 W/m.K for dry wood when I was looking at heat loss, a value that I got from here: https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html I think (that gives a value of 0.147 W/m.K for dry wood across the grain). I collected together some lambda values for building materials in this list, that may help: Link to comment Share on other sites More sharing options...
Ed Davies Posted February 9, 2020 Share Posted February 9, 2020 1 hour ago, Alslo said: They are saying U value for softwood is 1" =0.64 Are you sure? Americans tend to give the thermal properties of materials as R value/inch so I suspect this is that. Give us a reference to the source and we can work through the conversion from firkins per fortnight or whatever it is. R value is the resistance so 1/U value (which is the conductance). R value/distance is the resistivity so inverse of the conductivity which often written as k or λ value. Actually, the Americans are more sensible in giving the resistivity of materials as usually you want to find the resistances of all the layers in the wall, roof or whatever (by multiplying the resistivities of the layer materials by the layer thicknesses) then adding those up and taking the inverse to get the U value of the whole build up. Link to comment Share on other sites More sharing options...
Ian Posted February 9, 2020 Share Posted February 9, 2020 @Alslo be careful you don’t mix up K-Values, R-values and U-values when doing your calculations. If the K-value of timber is 0.15 and you have a 380mm thickness as in your 15” thick timber logs then the R-value will be 2.54 m²·K/W and the U-value will be 0.39 W/m²K Link to comment Share on other sites More sharing options...
Alslo Posted February 10, 2020 Author Share Posted February 10, 2020 Thanks for all your help. I will get a chance this evening to have another go. Link to comment Share on other sites More sharing options...
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