radiator but and wat for an A3 house

homewardbound11

I am trying to source information for radiator calculations for an A2/A3 house. The current calculations of lenght by breath by height times 40 for wattage may be an issue.
Is there anywhere that i can get this information to work out the radiator sizing
Regards,
Homewardbound11

Micky Dolenz

Do you know the u valves for the floors, walls, ceilings and windows? If so, a mears caculator will give you an accurate calc. Allow 12000 BTU's for a 300L cylinder approx.

Joey the lips

Micky Dolenz wrote: »

Do you know the u valves for the floors, walls, ceilings and windows? If so, a mears caculator will give you an accurate calc. Allow 12000 BTU's for a 300L cylinder approx.

Its up to the individual but I was thought to allow 2000 btus for hot water. But I dont wish to sound padantic.

Micky Dolenz

Joey the lips wrote: »

Its up to the individual but I was thought to allow 2000 btus for hot water. But I dont wish to sound padantic.

2000 BTU'sd per hour wouldn't heat a whole pile. Normal immersion's are 3KW, 3000 Watts or 10,250 BTU's. So allowing 12000 should be enough to heat and keep heated.

Joey the lips

Micky Dolenz wrote: »

2000 BTU'sd per hour wouldn't heat a whole pile. Normal immersion's are 3KW, 3000 Watts or 10,250 BTU's. So allowing 12000 should be enough to heat and keep heated.

Sorry that was ment to be 20000 as in 20k.

homewardbound11

Hi Micky,
yes, I have completed a preliminary BER and the average Uvalues for floor walls,roof are .17, .13 and .11. Mechanical ventilation and tripple glazing with window u values of 0.89. Front door is 1.2. I have a 300L SS solar cylinder using 4 flat panels.Timberframe construction with 235 studs filled with cellulose and 50mm of rockwoll filled cavity. Air tightness already under 2 ach/hr at Q50 and expected to improve.
This question just popped up tonight and my plumber has not worked with such a house before. I have the xml draft for the deap calcs. Calculated kw boiler required is 15kw to cover this house. heatloss is 50kw or there abouts

Regards,
Homewardbound11

Micky Dolenz wrote: »

Do you know the u valves for the floors, walls, ceilings and windows? If so, a mears caculator will give you an accurate calc. Allow 12000 BTU's for a 300L cylinder approx.

Micky Dolenz

Joey the lips wrote: »

Sorry that was ment to be 20000 as in 20k.

Thought as much. Probably down to the fact cylinders and pipework are insulated better so don't need to be overestimated. Oversizingcan be problem when calculating modern systems.

homewardbound11 wrote: »

Hi Micky,
yes, I have completed a preliminary BER and the average Uvalues for floor walls,roof are .17, .13 and .11. Mechanical ventilation and tripple glazing with window u values of 0.89. Front door is 1.2. I have a 300L SS solar cylinder using 4 flat panels.Timberframe construction with 235 studs filled with cellulose and 50mm of rockwoll filled cavity. Air tightness already under 2 ach/hr at Q50 and expected to improve.
This question just popped up tonight and my plumber has not worked with such a house before. I have the xml draft for the deap calcs. Calculated kw boiler required is 15kw to cover this house. heatloss is 50kw or there abouts

Regards,
Homewardbound11

What is M2 of house? There are hundreds of free online calculators, try a few of them.

What boiler size are you looking at?

homewardbound11

M2 Sq is 292 (2 story). Boiler is oil condensing and it already is overspec'd at 21 kW. Large kitchen, family room,living room, 4 beds and 4 bathrooms. I will check up on the calc's online if. any suggestions appreciated.

Micky Dolenz wrote: »

Thought as much. Probably down to the fact cylinders and pipework are insulated better so don't need to be overestimated. Oversizingcan be problem when calculating modern systems.



What is M2 of house? There are hundreds of free online calculators, try a few of them.

What boiler size are you looking at?

scuzz

Hi homeward,
In the same position myself, need to size rads for a 15kw boiler with similar u-values in floor, walls, roof for an A3 rating Timber frame - 2900sq ft. The plumbing suppliers seemingly just do a basic calc for all and then oversize by a percentage. Also been giving varying opinions on whether rads should be placed under windows or not.

homewardbound11

I got word back from the SEI and they have asked for my BER assessor to reply. I am awaiting his input now..?.
From the SEI reply I gather the following

The total heat loss in your preliminary BER is your fabric and ventialation loss expressed in w/k.
Heat demand is calculated by multiplying the total heat loss by the maximum temperature differential (usually -1 to 21 therefore,22)
Add upto 4kw for water heating (2-4 depending on occupancy)
Multiply both by 1.1 and you get your dwelling space and water demand

So,,
Dwelling Space +water demand = (dwelling space loss *22+4000)*1.1

In my case (313*22+4000)*1.1 gives 11974W

Multiply this by 3.41 to get the BTU's of 40833.

+++++++++++++++++++++++++++++++++++++++++++++++

In working out the boiler requirement my assessor used a slightly different approach of
(a)Total window heat loss
(b)Total wall loss
(c)Roof heat loss
(d) floor heat loss

A+B+C+D Multiply by location factor of 26.5 This gives fabric losses
Volume of house (Floor area by height) by .25 by location factor gives Venitaltion losses

Ventialtion loss+Fabric loss+ 2-4Kw for water = Boiler Specification.

In My case
6422+5185+2000=13600W boiler or 13.6Kw Boiler.

It looks like the maxium temperature differential and location factor are the same thing.

But how the hell are Radiators being spec'd...

Best of luck and I hope someone who has experienced this issue could express their input./

Regards,
Homewardbound

scuzz

Homeward,
I got a similar response and in relation to the rads I was told the following:-

For dwelling heat load, the maximum space heat demand is calculated by multiplying the heat loss
coefficient by the desired maximum temperature differential (deltaT usually -1 to 21 degrees C). The heat loss
coefficient is the heat loss in W/K of the dwelling when accounting for fabric and ventilation losses. The heat
loss coefficient is called the "Total Heat Loss" in the DEAP.
2 to 4 kW should be added to the space heating demand for water heating depending on occupancy or floor
area.
The total of space and water heating requirement should then be multiplied by 1.1 to account for
distribution losses giving the following maximum recommended dwelling heating load:
Dwelling space and water heat requirement (W)
= dwelling space heat loss + dwelling DHW requirement
= Total Heat Loss*22 *1.1 + 4000*1.1


It was recommended to include DHW in sizing the boiler as during the winter the boiler will have to do both space and water heating.

To suggestion to size the rads was to take the total heat loss and pro rata it for main floor areas down stairs and upstairs and apply the same equation above minus the solar.. The figure you will get will be in Watts so divide by 1000 to get the kW size of the radiator.


On a seperate issue what type of insulation are you using under the slab, I am going with the aeroboard platinum as i have succumbed to the scaremongering on the polyurethane products.

Regards
Scuzz

homewardbound11

Hi Scuzz,

I have had my plumber out and he wants to specify Length by Breath by Height times 4. As he said, he has no idea how to specify a low energy home. My Ber assessor was unable either to help me with only suggestions to alternate on line calculators.
There appears to be a serious lacking in knowledge in this area in ireland both on a professional level right down to the installer.

So with that it looks like i have no other option but to be a guinea pig for other installers. Ridiculous, god forbid that an installer would actually have to research the knowledge himself for his own profession. Lets hope the days of the easy money ends quickly and they actually earn their keep.
Sorry for the rant but it is exactly what is happening out there.

Micky Dolenz

Have you asked your installer to do calcs using a mears calculator?

Any decent installer should have one. Have you thought about changing installer?

JohnnieK

The outside temperature should be taken as -3oC, That's what I was thought in collage.

The installer should be able to calculate the heat losses unless he is old school and using the old BTU method, if this is so the rads will be over sized for the area.

If it is a low energy house you will have to get the U-values because they would be lower than the norm, and the installer would only be guessing at them using industry standard ones unless he knows how to make up the U-value using product data sheets which I doubt.

Why dont you hire a Mechanical Engineer to work all this out with your installer, I'm sure there are plenty screaming for work out there.

homewardbound11

JohnnieK.

I already have the heat loss from my BER calcs, If needed i have the u values also . It looks like my plumber is old school and does not have an uptodate mears calculator. I really thought my BER company who specialise in informed decisions for heating systems would have had this information.

So, if I now look for a mechanical engineer, what fees would it be to specify the radiators. ??
Do plumbers normally keep an upto date mears calculator or is this something for their school days.

JohnnieK

Do you have the heat losses per room or for the whole dwelling?
The BER assessor should have calcs for each room!

homewardbound11

Hi Johnniek

I have just gone through the detailed report and there is no heat loss for each room only total heat loss . . I have the xml file at hand and attached.( Please change .doc to .xml to open it with an xml viewer.)

I have the following tables/results

-)whole house boiler sizing (13kw boiler)
-)Ventilation details
-)building elements
-)Windows
-)Tota heat loss report (313 W/K)
-)Water Heating
-)Solar water heating
-)Lighting +internal gains
-)Net Space heat demand
-)Space heat demands in calander year
-)Distribution losses
-)Energy Requirements
-) Summer internal gains
-) Results.

JohnnieK

Hi Homewardbound11

The assessor would not have been able to come to the conclusion of the whole house heat requirement for the boiler with out getting the kW value for each room. There is No way. So some where in his office he has the calculations.

I dont understand his report! to go to the bother of calculating each separate space to only come up with a total requirement for the house on the report.
The btu method will over size the rads but not by a huge amount, and assuming you will have TRV valves on the rads this should not be a major issue. If this is an oil fired boiler we are talking about specify a Grundfos ALPHA2 pump, this pump is modulating and will react to the system as radiators and valves close down.

If you are certain you dont want to go down the btu route it could mean getting a plumber who can do the installation calculations using today's method's.

John

homewardbound11

Hi,
Just an update. I am going to meet an M&E engineer tomorrow eve and the upshot is that they dont use total heat loss as their sole calcs. A rule of thumb for low energy houses is 35w per m2. I am going to go and sort this one out tomorrow as i believe it still is marginally high. but anyone not going to the hassle of all this it seems that 35 is a basic assumption.


it is not far from the L*B*H in feet times 3.5

scuzz

Hi Homeward,
Good stuff, would be interested in your findings.
Also found this online maybe worth a look:-

http://www.rusfa.com/
Has a basic and professional radiator calculator at a cost

This program calculates the heat losses on a room by room basis and creates a schedule of rooms, heat losses and radiators.


Easy to input details of building elements.
Calculates ventilation losses for user-defined air-change rate.
User defined internal and external temperatures and relative humidity.
Incorporates combined method U-value calculator for walls, roofs, floors, doors and windows. The easy to use U-value calculator has a database of commonly used materials, with facility for user to modify.
Allows user to input chosen radiator type and size.
Schedules and adds up the heat losses and radiator outputs for up to 20 rooms. Larger projects can be split up into two or more files, e.g. Ground Floor and First Floor.
Gives approximate total heating load for boiler sizing.
Easy to select suitable boiler from SEDBUK boiler database using BoilerBrowser which is now fully incorporated into the program.

JohnnieK

How did you get on?

homewardbound11

Hi,
O.K. I met with my mechanical engineer and 35 watts is used as norm . To compensate for over heating trrv's are used on all rads and an electronic pump to control the pump speed. ths will have the effect of slowing the flow through the remaining radiators.
Btpass valves should be used local to the boiler in the event that all trv's shut down and prevent any flow
So in short control will compensate for overspec'd systems.

Micky Dolenz

homewardbound11 wrote: »

Hi,
O.K. I met with my mechanical engineer and 35 watts is used as norm . To compensate for over heating trrv's are used on all rads and an electronic pump to control the pump speed. ths will have the effect of slowing the flow through the remaining radiators.
Btpass valves should be used local to the boiler in the event that all trv's shut down and prevent any flow
So in short control will compensate for overspec'd systems.

35 watts per M2?

Out of interest, how much did your ME cost you?

rj2010

Just wondering what did you decide to do in the end and how is it working out for you? having similar queries regarding my own build at present

many thanks