I would advise getting the system designed/specified by a professional so you have some come back if it doesn't perform.

Thermal store with that set up?

That's what a SAP assessor does, with training, and takes a few hours maybe. So non-trivial to get it reasonably accurate I think, though not impossible.

Rgds

Damon

Posted By: wookeyTo get a really accurate estimation you need to use PHPP (which costs 140 quid). That's almost certainly overkill.

Or use something like hot2000, which is free and does a whole-year simulation based on weather data for your region. It might be overkill, but the models have been validated against real test buildings.

Paul in Montreal.

Posted By: roseramblerworking on a spreadsheet room by room

Good for you, roserambler, I have done much the same. Main reason for using a professional is to have someone to blame.

It's not a disaster if you are a bit generous with your design. Your system may be slightly more expensive than absolutely necessary. But you are not condemning yourself to higher fuel bills. The thermostats will throttle down the rads and boiler as required.

Professionals cut their calculations fine because the customer is comparing quotes, so the difference between an 800W radiator and a 1000W radiator may lose the installer the job.

Evan / rhamdu,

Iam making good progress. I have learnt a lot from this site and now putting into practice. Have set up spreadsheet for each room and now have estimated heat loss room by room. Can someone cast an eue over the assumptions finding to make sure not hugely wrong:

Assumptions made are (and I have urred on side of caution with numbers:
Roof: 150mm kingspan with breathable membrane U-Value: 0.3
External walls: 450mm stone / rubble with 25mm(insultaion PUR) platerboard U-Value: 0.7
Floors: Solid concrete (700mm) with 100mm kingspan PUR: U-value 0.3
Double galzed cat A windows: U-value: 3

For a two story detached house of 190 sq m 4 beds at first floor (west - east orientation in protected spot) with refurbished spec as above I have estimated overall heat loss at 11,000 watts.

Large end ground floor rooms (16sqm) 1500w
Mid size bed (1st floor) 11 sq m 600w
Large bed (3 external walls) 16sq m 1200w
Small study 1 external wall 9 sq m 450w

Proposing a Mitshibisi ASHP 14KW (3 KW over estimated heat loss). aiming for 45c flow rate for rads and 30c for UFH. total rad load 6700w total UFH load 3,300w. Back up space heating in coldest room and main living area with small woodburning stove (6KW).

Any views?

Thanks Rose

Evan: I think my SAP survey assumed my ageing DG to be 2.7W/Km^2 whole window, ie about ten times as bad as my newly-aerogelled walls...

Rose: I have our rad flow temp at *about* 50C and I've pushed it up a bit to maybe 55C in bitter weather, and that's with reasonably modern double-skinned rads.

Rgds

Damon

Help!

I have just had the plumber round who has estimated the heat loss for bed 1 at 1900watts using a revolving multi layer plastic 'trade' heat loss calculator. I estimated it at 1,140watts. I really need to know who is wrong here cos the whole heating plan of an ashp etc is under threat.

Now I have made up a detailed heat loss spreadsheet based on info taken from this site and other areas. If he is correct - it means the heat load for the whole house is incorrect and the 14KW air source heat pump will not be adequate to heat the house. I am just about to make the financial plunge - so can you please help me.

I have set out below the spec for the room below and the assumptions used. If I am close, then I guess I am ok - and he has been fiting rads 70% too big in well insulated houses!. If the plumber is close, I am looking at an oil condesing boiler!

i) Walls 450mm stone rubble 20 sq m. To be dry-lined with insulated by 30mm PUR insulated plaster board. estimated u-value 0.7 Temp difference 20 c.

ii) Internal walls: 15sq m Plasterboard with 100mm of rockwall inbetween . temp difference 0 degrees.

iii) Roof over 150mm of kinspan PUR in a vaulted - A - design ceiling. An extra 200mm of rockwooll inbetween rafters on flat part of A in roof structure. temp difference 20c estimated U-Value 0.3

iv) Windows Double glazed UPVC good quality cat B. 2 sq m. Heat difference 20 c estimated u-value 2.5

v) Floor: 18 sq m area: 200mm of rockwool with 30mm insulated plasterboard under. temp difference 15.

vi) room cubic capacity 18 x 2.4 = 43 sqm

Fabric heat loss 588

vii) ventilation loss: 2 air changes, 22c temp change, 0.33 ventilation factor (estimated vent heat loss 551)

Total room heat loss 1140

How far out am I? Your help is really appriciated

rose

Your figures look reasonable to me, in fact you are a bit pessimistic with some of your U values and 2 air changes might be high for a bedroom as well.

However, you've used a low value for the temperature difference; I would expect heating designers to use something like 25C, which increases the losses to about 1440 watts. The plumbers rule of thumb calculating device is probably using pessimistic U values as well, which will increase his heat loss guesstimate.

This could be the problem:

Am I confusing heat loss - which seems ok based on your kind comments with rad sizing. I was assumming that if the heat loss of a room was say 1000watts, allowing for a bit of leeway - I was looking for a radiator with a heating output of say 1200watts. What is the rule / guidelines for converting heat loss in watts to heat output for radiators in watts?

Thanks

rose

Posted By: wookeyHeat loss calcs are simple (if you use the standard 'assuming steady state' arrangement). You can take the simple 'whole house' approach or do it per-room. Whole house is very simple. Worksheet here:
http://www.energysavingtrust.org.uk/Publication-Download/?p=1&pid=229

Tried to find this and failed. Does it still exist?

Not for the simple case, no: you can do a perfectly good approximation for normally-constructed houses without it. You can do an official one (not necessarily any more accurate) with SAP. PHPP comes into its own for well-insulated buildings where you start to really need to account for thermal bridging and psi values and solar gain.

I'm part-way through modelling my house in all 3 (DIY spreadsheet, SAP and PHPP) to see how that works out for a typical 1960s house, before and after retrofit. But this is somewhat stalled currently by trying to finish building things :-)

Yes looks like EST have taken their calculator away.

These people do some windows software for the same methodology:
http://www.daikinheating.co.uk/for_professionals/for_installers/technical-tools.jsp

Here is the sedbuk version, which I suspect is the same thing: http://www.sedbuk.com/whole_house.htm

You can download the worksheet and do it ona piece of paper! (remember them?) (it's not hard):
http://www.rebelenergy.ie/ce54.pdf

There is an online US one but that makes you work in BTUs and Farenheight - (yuk) and no doubt uses ashrae assumptions or something:
http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

We badly need someone enthusiastic to write a toolbox for all these collected 'simple sums' things. I'm enthusiastic but it's quite a long way down my to-do list at the moment.

Posted By: Paul in MontrealDon't forget about hot2000

can't get that link to work.

Posted By: borpincan't get that link to work.

Seems their webservers are having a problem - I've sent an email to the support people. hot2000 will be able to do all you need.

Paul in Montreal.

And here's the list of features:

HOT2000 Features:
Ramp up your design capability and productivity quickly using the:

Intuitive graphical user interface and a visual directory tree to simplify inputs and give you direct access to specific ceiling, wall, floor, foundation and HVAC system screens – it also covers electrical base loads and hot water systems
Projections of space heating load and monthly and yearly energy requirements, taking into account utilized solar and internal gains
Full analysis capability in Imperial, U.S., or Metric (SI) units; and includes climate data from hundreds of Canadian and U.S. cities, as well as selected centres outside North America
Instant access to context-sensitive pop-up windows to define and explain each field, plus a full set of built-in help files to give you all the details
Technical reports for full-house, selective house (customized) and multiple house technical assessments, including site-specific data, fuel-cost data and detailed monthly tables

Model:

Electric, natural gas, oil, propane and wood space heating systems and domestic hot water (DHW) systems
Space heating and DHW systems from conventional to high-efficiency condensing systems
Air, ground and water source heat pumps
Central air conditioning systems with conventional or economizer controls
Primary and secondary DHW systems, including solar DHW
Inputs of steady state or seasonal efficiencies for heating and cooling equipment
Solar gain through windows in 8 cardinal directions
Tilted windows, including skylights
Overhangs, taking into account the hourly position of the sun with respect to each window and overhang on a typical day each month
Various levels of thermal mass
Slab-on-grade, crawl space (open, ventilated or closed), basement and walkout foundations, taking into account: dimensions; resistance and placement of insulation; soil conductivity; water table depth; and weather/climate
A house as 3 zones - attic, main floor and foundation - taking into account the heat transfer between zones

Calculate:

The seasonal efficiency, based on the characteristics of the specified house, for:
space heating systems, including part load curves and on and off cycling; and hot water tanks, including hot water load, standby losses and location
Heating and cooling loads on the basis of house design
Design heat loss rates for space heating system sizing
Fuel consumption and costs
Effective R-value of envelope components, including thermal bridging of the framing materials
Effective R-values of attic ceiling structures, taking into account insulation compression at the eaves
Effective R-value of windows, including glass type, fill type, spacer and framing
A typical Energy Rating (ER) for each window type
Utilized solar and internal gains
Heat gain arising from insolation, exterior roof and wall color choices

Model Air Infiltration and Mechanical Ventilation:

Models central ventilation systems, including heat recovery ventilators (HRVs) and fans without heat recovery
Models secondary supply and exhaust fans
Enter actual blower door test results or select one of HOT2000's pre-defined air tightness levels
Accounts for stack and wind effects and their interactions using AIM-2 (the Alberta Air Infiltration Model-2)
Accounts for the interaction of air infiltration and the mechanical ventilation

Report:

Technical report, including monthly tables
Comparison report for comparing results on up to 4 houses simultaneously
Weather, fuel cost and economic reports

Added Features:

English and French software versions
Climate data files on 75 Canadian and 200 U.S. centres, plus the option to create user-defined weather files
House templates - predefined files with default values that can be used to fill in commonly used data automatically when creating new house files
Multiple views for editing data
Global editing feature
Fuel costs editing feature for established utility rates
Economics editor for analysing and comparing conservation investment options between 2 houses
A graphical user interface for Windows 95 or Windows NT
A visual tree directory for navigation
On-line help files
Context-sensitive help
Defaults
Metric, imperial and U.S. units of measure

I entered the model for Tony's House ... using standard UK construction material. You can create your own wall build-ups in hot2000 - there's enough choice of elements that it should be easy enough to create something that's close to UK standards.

Paul in Montreal.