G and J

I guess I want the formula behind the annual heating demand row in your spreadsheet.

Very interesting and useful stuff @MikeSharp01, thank you. I’d grasped the principles of load vs demand but it’s details like TFA and perhaps a rough and ready calc method I was seeking to get a feel for how far short of passive we will end up being. ’Near passive’ is a term used on here but I am interested in quantifying how near. Maybe I’d be better of not knowing and staying deluded lol

I thought my heat load as measured at -10c and with 148m2 of floor is 2500/148=16.9W/m2 which is not so good compared to the PH target of less than 10W/m2. I was also hoping to be able to calculate what I think is called total heat demand which is measured in kWh per m2 per annum. Maybe I need to raid me piggy bank to buy a PHPP license to find out, but as it’s only of passing interest I was hoping there would be a way of deriving a credible estimate.

Fab discussion. Very illuminating. But I still don’t know how to calculate total heat demand. 😞

Agreed, but I didn’t want to assume that the heat load calc assumes that too.

Our MCS plumber dude told us straight of that the smallest heat pump we can have will be oversized, so I kinda took that as a given but corroborating opinions are useful. I was trying to calculate heat load/demand to get my head round how far off passive standard we are. With the current set of assumptions I’m working to at -10c the heat loss divided by the internal floor area is around 17W/m2, so we are well over. At the Norfolk level of -2.3c it’s 13W/m2 ignoring DHW - and just over 14W/m2 if I do the patent @JohnMo 24/22 DHW fudge factor - which doesn’t look so bad after all. My confidence level in these numbers though is not high yet as I have the queasy feeling that I’m missing a basic, partly because they are so much better than I naturally expected (I still associate passivehaus with long straggly beards and 4’ thick cameldung and candyfloss walls, but then, I am an old reactionary at heart!). Heat demand though still confuses the life out of me.

Ta for the link - won’t let me register at the mo but will keep trying.

So, guess who has been up late googling..... I found the following on an Australian website (I think it still works even though they are upside down over there): "While the building heat load tells you how high the boiler output needs to be, the heat demand indicates the amount of energy that is required per square metre over the course of a year. The heat demand or building energy demand is therefore a criterion for describing the energy quality of a building." Makes perfect sense. So if i look at Jeremy's spreadsheet it calculates the heat required to maintain the internal temperature - default is 20c inside and -10c outside which gives me ~2.5kW. But.... I'm not sure if -10c is excessive for Suffolk, There's no allowance for getting up to temperature, and There's no allowance for hot water either. And I'm really not sure how to derive the heat demand figure from his spreadsheet. Help!

Brilliant link. Thank you.

I’ve filled it in and I continue to play with it on a ‘what if’ basis. And yes, I’ll be very embarrassed if both figures are there already and I’ve failed to notice! (But I’m ready. I’ve my own conical ‘D’ hat and a stool waiting in the corner!)

Dear Buildhubbers, I’ve been trying to find a formula to estimate our house design’s heat load and heat demand, but the combined intellect of google and me have failed. Please can someone enlighten me. Regards, Confused of Suffolk.

In previous lives (well, when I was working) I encountered no end of folk who knew their calculations were correct and relevant because they had a spreadsheet that calculated numbers to 3 decimal places, or the like. So I’m with you on that one. Often an informed guess beats the calculator.

That’s certainly my impression. If you look at the engineering involved they should be less than £100 a pop but the volume isn’t there yet.

As someone wrestling with wall thickness vs room size I sympathise. I’ve been experimenting with Jeremy’s heat loss spreadsheet and actually insulation cost vs heating cost payback is much worse than I expected, specifically meaning that after a certain level extra insulation just doesn’t pay back sensibly….. But! I’ve a horrible feeling that if I design by spreadsheet I might get the optimum financial balance but will I get the most comfortable? I guess that might simply translate for the OP into a bit of central heating rebalancing.

OK, I’m officially confused. That doesn’t look like a clever zero volt switch. If you’ve only got a two core cable back to the ASHP then presumably that’s just on/off, so how does the pump know whether to cool or heat? I’ll take deep breaths and try and stay calm whilst hoping for a comforting circuit diagram to ease my perturbations.

And ever it is thus. It seems the minute we buy anything they bring out a better one which is kinda annoying but that’s progress. Except sometimes ‘better’ is just different and it does the same job. C’est La vie.

I’ve that ‘I’m being dumb’ feeling but please could I see a circuit diagram of the above.

Meaning I can’t just use a normal physical switch, or at least, I then have to use it through another zero volt switching device. I'm guessing this is to protect vulnerable components in the heat pump?

So it presents different connections for above and below set point, and you use that to switch between heat and cooling mode. If so, in winter if you light your woodburner (you might have to instal said woodburner first), the system could then go into cool mode.

What stat are you using?

Methinks the hard part will be the control system, especially the user interface. I hope to use the DAF model based on a single switch (instead of the gear knob). Heat-Off-Cool. I might make it look clever by having a bank of flashing lights and some 50’s Ipcress File computer type noises alongside said three position switch, maybe even an “Achtung! No Gerfingerpoken! Verboten!” sign in red letters too. This will be above a non-latching, push to make switch behind a really big red button labelled “in case of nuclear fall out, steam or excessive farting, press once” which will be the user interface for the MVHR.

Has that got 3 connections (common, no, & nc I mean)?

That’s how we will start, and hopefully stay. If faster cooling is needed the valves and a volumiser will be added laterer.

Sorry about the delay, wanted to have a quick word with them before I posted. It’s a company called Heat, Space and Light.

Yep, two storey our bedroom upstairs and not huge solar gain as not huge windows and few south facing. I’m now erring towards a single zone UFH and fancoil run just above dew point as per @JohnMo. So at least I’ve got someone to blame lol I could mount an A2A cooling unit in our cold loft, I guess I’d worry about noise and servicing it, as it’ll be a crawl through fink trusses by the time I’ve laid all the insulation up there with some crawl boarding on top.