Heat loss calculations

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OLD

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I have a long term plan to replace the central heating but because i am 9 inch brick that is difficult to insulate and want a system that gives a even heat . I would like to do the loss calcs. is there a book ,software or other resource available please.
I see there is info on google but a personal recommendation is what i need .
 
Old

Curious to understand where you're coming from on this and what's prompted you as replacing the central heating system is not for the faint-hearted as I'm sure you already know.

Is it that certain rooms are colder than others? Or is it that the radiators aren't heating up enough? You see where I'm coming from is that it might be that a decent power flush and system clean might be a quicker solution and much cheaper!

As dibs-h has said it depends on the accuracy that you want to achieve. For example, there are several calculators on the web that simply do a whole house calculation but don't go down as far as individual rooms. To go down to the individual room heat requirements you need a calculator that takes into account the six elements of each room (four walls, floor and ceiling), the u-values of those elements and that of any openings like windows, and the heat losses and gains to/from those elements from adjacent elements. Then add in a factor for ventilation change and another for domestic hot water. i did create a spreadsheet but have no idea where it went to sadly. i could dial in individual design temperatures for each room/element to simulate real life and then see what the effect would be in terms of heat requirement on adjacent rooms. For example, running the sitting room at 20 degrees dropped the heat requirement for the bedroom above quite considerably as that room gained from the heat coming from underneath.

But I do come back to my earlier question as to what is prompting you. Reason being that I've just gone through/am going through the same exercise. Maybe I/we should make it a feature in the project section :wink:

Then to do it properly (apologies if this is grandma and eggs time) is to work out how you're going to run the pipes - perhaps there is a better way than was done previously - calculate what the heat load is of each pipe run, factor in the losses due to right angle bends and couplers etc and that will then give you the size of pipe that you need to feed the radiators connected to them. Many central heating installers don't bother to do that.

When I installed my current ch system, I started with 35mm coming out of the boiler then gradually reduced to 28mm feeding a rads and a few branches of 22mm which then fed more rads and then more branches of 15mm for some of the runs.

Then you need to decide if you want an S plan or a Y plan.

I'm in the process of replacing my 18 year old boiler with an external one, replacing the hw cylinder and thermostat (because it's probably furred up after 20 years) and I want to put in place an 'intelligent' secondary return for the domestic hw as there are too many deadlegs. The latter was another design decision and on balance I screwed up on the economics and should have gone for a combi external that fed hw to the downstairs taps from the combi supply but left the rest of the system vented with the hw cylinder.

Sorry to have rambled on a bit.

Roger
 
RogerS":2z6kooyr said:
Old
To go down to the individual room heat requirements you need a calculator that takes into account the six elements of each room (four walls, floor and ceiling), the u-values of those elements and that of any openings like windows, and the heat losses and gains to/from those elements from adjacent elements. ..

I had one some time ago where it would allow for a large number of layers in a "wall" and catered for bridging and all sorts. Very thorough to say the least - but sometimes it was just easier to go for a nominal value as opopsed to a more accurate one.
 
Dibs-h":jt4mhkmp said:
RogerS":jt4mhkmp said:
Old
To go down to the individual room heat requirements you need a calculator that takes into account the six elements of each room (four walls, floor and ceiling), the u-values of those elements and that of any openings like windows, and the heat losses and gains to/from those elements from adjacent elements. ..

I had one some time ago where it would allow for a large number of layers in a "wall" and catered for bridging and all sorts. Very thorough to say the least - but sometimes it was just easier to go for a nominal value as opopsed to a more accurate one.

:D I know and the more detail the more you believe the figures ! While trying to calculate the size of boiler I needed for the replacement, I did the whole house calculations (two different versions) and both came out with around 26kW. I then added up the actual heat that the radiators I put in could actually pump out and then added in a figure for dhw. Guess what? 21kW because I undersized the rads as I'm a bit of a cheapskate at times. Also explains why some people find our house cold!
 
Thanks for the info above. The pipe work is 40 years old the boiler 20 two pipe to upstairs and single buried in concrete floor down stairs. Down stair system has difficulty coping with very cold weather and heat is not that even normally .I would like a combi boiler to get rid of cylinder and tanks so that the bath room can be rearranged and shower cubicle installed. Its all looking like a big job and this is the start of my design process.
 
How many folk live in your house, Old? Combis do have a reputation of not being able to deliver adequate hot water for everyone at the same time - but I'm sure you've heard of that.
 
Old,
If you want to PM me i`d be happy to do the heat requirement calcs for you. I`m doing a load in the next week, so a few more rooms won`t make a lot of difference.
 
If you do go down the combi route and also do the work yourself I have a pressure tester that you are welcome to borrow. Believe me, you will need one especially if the pipes are going to be hidden. DAMHIKT
 
Other thought before you get too wedded to a combi is to get a bucket of known volume and time how long it takes to fill. Some combis specify a minimum flowrate that must be provided. Also you can then work out how long it will take to fill your bath (assuming no-one else is drawing off hot water at the same time) and see if that is acceptable.

Other combi thoughts are:

power showers - don't believe that you can have them with a combi. Have you got enough water pressure and flow rate (the two are not the same thing) for a decent shower ?

what will you do for hot water when the combi packs up? No immersion heater after all.

Avoid Baxi.

Copper pricing seems to be going through the roof. Consider plastic central heating pipe (personally I prefer Hep20) although you need to have copper within 1000mm of the boiler. Also not all combis allow plastic pipes (Worcester Bosch does not. Warmflow does).
 
Doug B Thanks for the kind offer i have just received a calculator program from ebay by the heating and hotwater info.council seems ok so i can now do the calcs.

RogerS Thanks also for your advice and offers of help as i said this is just the start or my plans so i may have to come back once i have firmed them up.

Dibs-h The calculator i have now does calculate all the elements as you sudjested thanks for the guidance.
 
OLD":2rjsx5de said:
Doug B Thanks for the kind offer i have just received a calculator program from ebay by the heating and hotwater info.council seems ok so i can now do the calcs.

RogerS Thanks also for your advice and offers of help as i said this is just the start or my plans so i may have to come back once i have firmed them up.

Dibs-h The calculator i have now does calculate all the elements as you sudjested thanks for the guidance.

Does it allow you to calculate the U-Value for a custom "wall", that isn't in the drop down selection?
 
Dibs-h The application cost £7.49 inc. its version 3.04 the latest is v4 .No custom walls but 21 external drop downs and 9 internal drops which cover my situation ok.From the calc i have done existing radiator sizes are way out
 
Just a update on my deliberations, the combi is out. Had a plumber visit me last night and he pointed out the water pressure was marginal and we would have to learn to live with the time lags.So as the bathroom needs the extra space we have to reposition tanks and cylinder and take the opportunity to improve the control of what will become a fully pumped system the rest of the modifications to the central heating are calculated and look straight forward, so some progress.
 
I ripped out our antique Glowworm spacesaver recently (weighed a ton - took 2 of us to get it out). Replaced it with a re-branded Volkera combi - not ideal but as there was no labour and the boiler cost < £500, the payback should be rapid.

The final solution will most likely be a heatbank and UFH with solar on the workshop roof - but that isn't on the agenda for approx 18-24 months.
 
Two points Old. What Rog says about the bucket is so right!
Two possible probs exist with a combi boiler,
one, they can be very unsuitable for a shower as frequently they will not heat enough water for a decent spray without a very much larger heat exchanger than is normally specified when purchasing for the CH requirements.
The spec will tell you that your chosen boiler will heat a given quantity of water in a given time through a given temp rise, where as that can be sufficient during the summer it can be much less so in the winter when the feed water temp drops.
You can of course look into a pressure tank to feed a shower but that adds to the cost.
Two, if you live in a hard water area I would forget the combi.

Roy.
 

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