degree days

[andrew]

I want to see if I can use degree day data to guestimate fuel use for a proposed steel frames and clad barn conversion, I want to decide the value of better than building regs insulation.

From what I can see a base temperature is specified at which the building needs no heat input, 16.5C seems to be the default. I take it that if internal temperatures are to be 19C then the loss across the delta T of

2.5C is made up from occupants' body heat and electrical gizmos being used.

So degree days below 16.5C need additional heat to balance losses through the fabric ( floor, roof, walls, doors and windows of known area and U-value) plus air changes. These losses are known in Watts/second but the degree day is an average and consists of 60*60*24 seconds. Is the annual heat loss a simple product of total Watts/ deg C for building times degree seconds?

AJH

[stuart noble]

I expect you've been here, but just in case...

[andrew]

date, in my location. Harry's answer suggests that this is normally used for comparisons and there is no direct correlation with predicting energy loss from a theoretical level of insulation.

It's a substantial building to be used by an environmental charity, of which I am a trustee. I'm keen it should be a low energy conversion and need to justify extra insulation cost. It will not be a DIY conversion.

On a conversion of a 13" solid brick walled building for new offices at work I wasn't able to get better than building regs (0.3W/deg C for walls and ceilings and 1.4W/deg C for windows) and though I have provided for Mechanical Heat Recovery Ventilation it's causing a problem with the floor plan. I wanted to justify this latter on the basis that I like a lot of fresh air circulation. I have just returned from an international conference, in a university lecture theatre, with some 150 delegates, I found I was constantly yawning and the room was stuffy and this did have forced ventilation. I also returned with a cold which I think I may have caught there and wonder if there is a case to be made for more rapid air turnover on health grounds?

[stuart noble]

I think it just allows you to compare heating costs by factoring in the weather.

[Andy Wade]

Losses (or gains) are in watts (joules/second) not watts per second.

Degree-days are a time integral rather than an average - effectively the product of time and the amount by which the outside temperature is less than the base value (and zero if above, for heating DDs).

How to use: Add up your individual U*A products and ventilation heat requirement to get an overall total heat demand in watts per degree of temperature difference. Then multiply by the degree-days for any period

- this gives the consumption for the period in watt-days. Multiply by

24/1000 to convert to the more useful unit of kWh.

The above was posted previously here:

[andrew]

I think if you remember back to sick building syndrome most of the problems were to do with ventilation, maybe I'm more sensitive and like more air changes because I was a manual worker, outside, for 35 years.

There are a number of interelated requirements:

1) minimum fresh air delivery of 8 litres/sec per person, 10 litres was required by our BCO and the window trickle vents can provide this as the rooms are small. I would need to relate that back to occupancy and room volume to see how this fits with your 2 changes/hour. 2) air velocities of

[Onetap]

On May 29, 2:16=A0pm, andrew wrote: . I have just returned from an international

I've been in one of those and spent the interval looking at the system. I was gobsmacked by the utter cluelessness of it.

I'd bet there was no fresh air; UK academia, run by over-paid bureaucrats who have to apply clueless penny-pinching to everything to justify their salary. Write out 100 times 'Split system cooling is NOT air conditioning'.

Many highly qualified academics flew in regularly to use that facility, not one of them could take in one word that was said because of the levels of CO2 that accumulated. The place I was in had a lecture theatre that could be divided by a folding partition. 'Our' half was full and we were cooking, so I turned down the temperature controller, that was in the 'other' half. The half-a-dozen 'others' were cold when they returned from lunch, so they turned it up.

See recommendations in the CIBSE Guide regarding fresh air provision for breathing and to dissipate odours. Should be available in a reference library. 16 l/s per person springs to mind. Or was that per minute???