Another heating question

Bobbiblu

I may have put the cart before the horse by asking the last question first but that don't matter too much I hope...

my question this time is how accurately can one predict the energy requirement for a house before it's built?

I reckon if you can supply a BER assessor (???) with the construction details of your house, from frame to insulation, to windows to HRV etc then they should be able to work out how much energy you'll require to have your space heated and your water warm....am I wrong here? or do I have to get someone really specialised to do this? or do I need to supply more info to whoever can do it? Or is there a more accurate way to do it?

Sorry for all the questions but like I said in my previous thread I'm looking for backup

Cheers!

sydthebeat

Bobbiblu wrote: »

I reckon if you can supply a BER assessor (???) with the construction details of your house, from frame to insulation, to windows to HRV etc then they should be able to work out how much energy you'll require to have your space heated and your water warm....am I wrong here? !

kind of.. yes.

The software the BER assessor uses is designed to compare dwellings o similar size and age, and cannot reflect your specific use of your building. It does make certain assumption and if you fall within these assumptions i suppose it can somewhat accurately predict energy usage.

for example DEAP (the software) assumes an occupancy population based on the floor area. It assumes temperatures of 21 deg in living room and 18 deg elsewhere. It assumes periodic heating up time scales.

what is your aim?

Bobbiblu

Great reply thanks syd,

my aim is to try to predict what energy we will need so as
a) we don't waste money on a system we could really do without
b) be uncomfortably cold in our house because we thought it would perform better than it does....does that make sense?

You see our house (on paper) ticks alot of the boxes for a low energy possibly even passive house so in my head I think it will take 'little' energy to heat it up in winter and once the heat is in the house with high level insulation & airtightness it should stay there right?. BUT at the same time I can't just go on a hunch that x heating system is or is not required....I'd rather be as informed as I possibly can be...so after a long winded response syd my aim is to be as well informed about how the house will perform as is possible before it actually starts performing....sim-ples

Bobbiblu

what about the passive haus software? I'm assuming that works on an individual house design basis or am I incorrect once again?
or do you have to aim towards to a certified passive house in order to avail of that?

sas

Bobbiblu wrote: »

what about the passive haus software? I'm assuming that works on an individual house design basis or am I incorrect once again?
or do you have to aim towards to a certified passive house in order to avail of that?

Use of the PHPP (Passiv Haus Planning Package) is very good idea.

The PHPP is a modelling tool that has a track record of accurately predicting the energy performance of a building.

It will successfully model a building to any energy level (assuming the tool itself is used correctly) so it is not specific to only passive houses, certified or not.

This could be the way to go.

Bobbiblu

sas wrote: »

Use of the PHPP (Passiv Haus Planning Package) is very good idea.

The PHPP is a modelling tool that has a track record of accurately predicting the energy performance of a building.

It will successfully model a building to any energy level (assuming the tool itself is used correctly) so it is not specific to only passive houses, certified or not.

This could be the way to go.

Nice one sas, on the ball as per usual any chance you could point me in the right direction as to where to get this done or how to?
Many thanks for the reply...

MicktheMan

Bobbiblu wrote: »

what about the passive haus software? I'm assuming that works on an individual house design basis or am I incorrect once again?
or do you have to aim towards to a certified passive house in order to avail of that?

I would recommend the phpp software to accuratly predict your energy usage and if you are serious about insulating yourself (excuse the pun!) from energy price rises in the future then this is the way to go. I see from the other thread that you are aiming for a well insulated, airtight house with hrv etc. Have you checked out what a passive house would cost extra to build (you might be pleasantly surprised) and what this represents in future energy savings? Imo, this could very well be the best investment you could ever make!

homewardbound11

Hi,
I have recently gone down this route in my self build of assuming that the preliminary BER calculations could be used to specify the heat demand of the house. With that the ber calcs supplied total fabric and ventialtion losses and was also able to supply the boiler requirements for the house.

This is where it stopped. Firstly the above information is only partially applicable to the heating system you use along with distribution losses and other factors. I hope my input is more or less what others are experiencing or have expressions on as it is based on the information i have gathered from 3 sources of professional input.
I am going with conventional radiators versus underfloor heating. I employed a ME engineer on top of my plumber and ber assessor and the mechanical engineer highlighted a senario. That you walk into your house, its cold, and you turn on the oil heating to your radiators. If you work to the DEAP calcs you will heat your house but not in the time required to satisfy you as you are going from cold to a comfortable 21 degrees in a timeframe. So using rads and oil senario, you will always over spec the system and also the radiators. You will then use control to compensate for the excess in the form of TRV's and bypass valves and boiler cut outs and electric pumps (pressurized systems).
Using underfloor systems where they are constantly always on I.E. geothermal you would work closer to the calculations as the heating system is always on and you don't have to compensate for the volume to be heated in a required time frame , only the volume to be heated agains the heat loss and requirement to maintain 21 degrees. So i guess underfloor is more about the distance between pipes and diameter and flow and return temps.
Using wood pellet is always spec'd less than a conventional oil burner as it too has a delayed responce due to burning process.
I hope my rant has made some sense but largely it depends on the systems used.
For a general observation from my ME engineer, he used 35watts per cubic metre for heating low energy homes of today.

sinnerboy

I think you'll find that's 35 watts per square meter Heat Load i.e. boiler / heat pump size . It's a pity you stopped where you did and did not look to use PHPP to advise on how to get the fabric better so you don't need to distribute heat by UFH or rads . If you can do so now you should . It is possible to supply heat via your ventilation system only if it's designed correctly . In context the Passive house max Heat Load is 10 watts per square meter

.

Bobbiblu

MicktheMan wrote: »

I would recommend the phpp software to accuratly predict your energy usage and if you are serious about insulating yourself (excuse the pun!) from energy price rises in the future then this is the way to go. I see from the other thread that you are aiming for a well insulated, airtight house with hrv etc. Have you checked out what a passive house would cost extra to build (you might be pleasantly surprised) and what this represents in future energy savings? Imo, this could very well be the best investment you could ever make!

thanks for the reply MtM, I've considered the passive spec many times but I'm sure I don't have the budget for it. However, I will keep reading up on it and do all I can to build as close to the passive spec as I can afford. I think you're bang on by saying it's a great investment building a passive house.
Plan now is to get the house spec put through the phpp software as suggested and see what sort of results we get. Will update when I have taken that step. Many thanks again for the advice.

L driver

I've considered the passive spec many times but I'm sure I don't have the budget for it.
Bobbilu,
Don't assume, passive may only cost a little more now depending on what you can do in the build yourself, but long term like over a mortage it's a winner. Do the figures it's a no brainer, get quotes. Everyone assumes passive is expensive, in this country it is easier to reach passive as we don't have extremes of temp. I wish I knew more about it before I started building now it is costing me time and some money to get as near to passive as I can. Spend a while on the net with passive house!