Heating vs dehumidifying

[John Cuthber]

9 hours ago, StringJunky said:

I found some numbers from a heating firm on most comfortable humidity levels at given temperatures.

For an outdoor temperature over 50˚F, indoor humidity levels shouldn’t exceed 50%
With an outdoor temperature over 20˚F, indoor humidity levels shouldn’t exceed 40%
Outdoor temperature between 10˚F and 20˚F, indoor humidity levels shouldn’t exceed 35%
For an outdoor temperature between 0˚F and 10˚F, indoor humidity levels shouldn’t exceed 30%
Outdoor temperature between -10˚F and 0˚F, indoor humidity levels shouldn’t exceed 25%
With an outdoor temperature between -20˚F and -10˚F, indoor humidity levels shouldn’t exceed 20%
Outdoor temperature at -20˚F or lower, indoor humidity levels shouldn’t exceed 15%

https://lauryheating.com/ideal-home-humidity/

That's interesting.
Surely the outdoors is outdoors and I shouldn't care what the temperature there is.
On the other hand, if I'm worried about preventing condensation, those numbers make more sense.

If it's 15% RH indoors, you will get problems of dry eyes etc.

[sethoflagos]

On 11/30/2023 at 6:35 PM, StringJunky said:

Scenario; A room has a temperature of 10c and high humidity.  We want to increase the comfort of the occupier. Is it generally energetically more economical to bring down the humidity or warm up the room a few degrees to increase comfort? 

Define 'comfort'

On 11/30/2023 at 10:37 PM, StringJunky said:

My comfort range is about 12-15c, if the humidity is not too high. Sat down I'll be in a jumper, but if I'm active a t-shirt is fine.

Okay, that's an unusally low temperature. Recommended humidity for occupied rooms is 40%-60% RH because reasons.

Air @ 10^oC and 100% RH contains 9.4 g/m³ moisture (calculator here)

Air @ 15^oC containing 9.4 g/m³ moisture is @ 73.3%  RH (same resource)

If its a contractual obligation job, then dehumidification seems obligatory. However, there are other considerations to bear in mind.

Maybe 73% RH is tolerable to you in which case, a modest addition of dry heat would do the job. Same if the initial humidity was more like 85%

If the room is humid only because of your breathing/perspiration and it's less humid outside then maybe all that's needed is a small fan to increase the ventilation rate a bit. Most typical occupied spaces are best served with ~7 air changes per hour or they can get a bit clammy. (Up to double that figure for say a computer room)

People are walking humidifiers emitting 6-7 MJ/day largely as moisture saturated warm air so there's major shifts in emphasis when dealing with small, busy rooms versus large sparsely occupied ones. 

On 11/30/2023 at 9:32 PM, swansont said:

Still, 50% isn’t particularly comfortable.

Guess it's down to the individual. Personally, I find 50% a bit on the dry side these days, but it is the standard target for the HVAC industry etc (eg industry source)

On 11/30/2023 at 10:24 PM, StringJunky said:

My portable dehumidifier is a desiccant type. The air that comes out is probably 3 or 4c higher in a 15' x 10' space. Consumption is 600w. Would 600w be fairly economical to makew the space what I call autumnal temperature; 14c.

600W of dry heat input would make a room this size quite warm quite quickly.

 

On 12/2/2023 at 3:16 AM, StringJunky said:

I found some numbers from a heating firm on most comfortable humidity levels at given temperatures.

For an outdoor temperature over 50˚F, indoor humidity levels shouldn’t exceed 50%
With an outdoor temperature over 20˚F, indoor humidity levels shouldn’t exceed 40%
Outdoor temperature between 10˚F and 20˚F, indoor humidity levels shouldn’t exceed 35%
For an outdoor temperature between 0˚F and 10˚F, indoor humidity levels shouldn’t exceed 30%
Outdoor temperature between -10˚F and 0˚F, indoor humidity levels shouldn’t exceed 25%
With an outdoor temperature between -20˚F and -10˚F, indoor humidity levels shouldn’t exceed 20%
Outdoor temperature at -20˚F or lower, indoor humidity levels shouldn’t exceed 15%

I checked the site and it does indeed say that.  Absolute nonsense.

These values are what would be required to prevent condensation on say the inside of a single-glazed window. Following this guidance would be a health hazard for any occupants. 

[studiot]

22 minutes ago, sethoflagos said:

Define 'comfort'

Okay, that's an unusally low temperature. Recommended humidity for occupied rooms is 40%-60% RH because reasons.

Air @ 10^oC and 100% RH contains 9.4 g/m³ moisture (calculator here)

Air @ 15^oC containing 9.4 g/m³ moisture is @ 73.3%  RH (same resource)

If its a contractual obligation job, then dehumidification seems obligatory. However, there are other considerations to bear in mind.

Maybe 73% RH is tolerable to you in which case, a modest addition of dry heat would do the job. Same if the initial humidity was more like 85%

If the room is humid only because of your breathing/perspiration and it's less humid outside then maybe all that's needed is a small fan to increase the ventilation rate a bit. Most typical occupied spaces are best served with ~7 air changes per hour or they can get a bit clammy. (Up to double that figure for say a computer room)

People are walking humidifiers emitting 6-7 MJ/day largely as moisture saturated warm air so there's major shifts in emphasis when dealing with small, busy rooms versus large sparsely occupied ones. 

Guess it's down to the individual. Personally, I find 50% a bit on the dry side these days, but it is the standard target for the HVAC industry etc (eg industry source)

600W of dry heat input would make a room this size quite warm quite quickly.

 

I checked the site and it does indeed say that.  Absolute nonsense.

These values are what would be required to prevent condensation on say the inside of a single-glazed window. Following this guidance would be a health hazard for any occupants. 

Nice to have an engineer casting his MK 1 eyeball over the figures.  +1

[StringJunky]

33 minutes ago, sethoflagos said:

Define 'comfort'

Okay, that's an unusally low temperature. Recommended humidity for occupied rooms is 40%-60% RH because reasons.

Air @ 10^oC and 100% RH contains 9.4 g/m³ moisture (calculator here)

Air @ 15^oC containing 9.4 g/m³ moisture is @ 73.3%  RH (same resource)

If its a contractual obligation job, then dehumidification seems obligatory. However, there are other considerations to bear in mind.

Maybe 73% RH is tolerable to you in which case, a modest addition of dry heat would do the job. Same if the initial humidity was more like 85%

If the room is humid only because of your breathing/perspiration and it's less humid outside then maybe all that's needed is a small fan to increase the ventilation rate a bit. Most typical occupied spaces are best served with ~7 air changes per hour or they can get a bit clammy. (Up to double that figure for say a computer room)

People are walking humidifiers emitting 6-7 MJ/day largely as moisture saturated warm air so there's major shifts in emphasis when dealing with small, busy rooms versus large sparsely occupied ones. 

Guess it's down to the individual. Personally, I find 50% a bit on the dry side these days, but it is the standard target for the HVAC industry etc (eg industry source)

600W of dry heat input would make a room this size quite warm quite quickly.

 

I checked the site and it does indeed say that.  Absolute nonsense.

These values are what would be required to prevent condensation on say the inside of a single-glazed window. Following this guidance would be a health hazard for any occupants. 

Thanks, Seth.

[swansont]

37 minutes ago, sethoflagos said:

Guess it's down to the individual. Personally, I find 50% a bit on the dry side these days, but it is the standard target for the HVAC industry etc (eg industry source)

Given the variability in results one can find, I don't think that's "standard." You can easily find sources that say 30-50%, or 30-40%, 25-60%, or 40-60%; each of these show up in the first couple of dozen results on Google. (and it's always a range, not a number)

My own experience was a couple of clock facilities with fairly tight control on temperature and humidity, with a target of 21 ºC and RH of 40% ± 3% and it always felt a little swampy. (Much lower RH meant a risk of electronics arcing, and above 50% risked mold, according to the lab/clean room design specs we had. They specified 30-50%, and we chose the middle)

Comfort comes down to personal preference and what you're used to.  

[sethoflagos]

1 minute ago, swansont said:

Given the variability in results one can find, I don't think that's "standard." You can easily find sources that say 30-50%, or 30-40%, 25-60%, or 40-60%; each of these show up in the first couple of dozen results on Google. (and it's always a range, not a number)

With respect, when I use the phrase 'standard target' I mean the middle of a range specified by the internationally recognised industrial design standards relating to a broad range of HVAC applications that I've been contractually bound to observe in the course of my professional working career. I do NOT mean 'the first bit of bs I found via google'.

These standards are in general not available outside of a paywall, so what source exactly would you wish me to quote? (My employers generally take my CV as sufficient authority. Would you prefer me to attach that? 🤨)

19 minutes ago, swansont said:

My own experience was a couple of clock facilities with fairly tight control on temperature and humidity, with a target of 21 ºC and RH of 40% ± 3% and it always felt a little swampy. (Much lower RH meant a risk of electronics arcing, and above 50% risked mold, according to the lab/clean room design specs we had. They specified 30-50%, and we chose the middle)

Electronic gear etc is not 'people'. Similarly, I've worked with slightly different ranges for long term paper products storage etc. The OP case is the OP case. @StringJunky is not likely to swell and crinkle when the air gets a little damp I trust.

[swansont]

22 minutes ago, sethoflagos said:

With respect, when I use the phrase 'standard target' I mean the middle of a range specified by the internationally recognised industrial design standards relating to a broad range of HVAC applications that I've been contractually bound to observe in the course of my professional working career. I do NOT mean 'the first bit of bs I found via google'.

OK, if you think professionals in HVAC/home improvement, ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) or NIST are considered BS, I can’t do anything about that, I guess

[sethoflagos]

Just now, swansont said:

OK, if you think professionals in HVAC/home improvement, ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) or NIST are considered BS, I can’t do anything about that, I guess

Strawman. I said no such thing.

Far from the first time you've responded in this way to my posts. Just saying.

[StringJunky]

39 minutes ago, sethoflagos said:

With respect, when I use the phrase 'standard target' I mean the middle of a range specified by the internationally recognised industrial design standards relating to a broad range of HVAC applications that I've been contractually bound to observe in the course of my professional working career. I do NOT mean 'the first bit of bs I found via google'.

These standards are in general not available outside of a paywall, so what source exactly would you wish me to quote? (My employers generally take my CV as sufficient authority. Would you prefer me to attach that? 🤨)

Electronic gear etc is not 'people'. Similarly, I've worked with slightly different ranges for long term paper products storage etc. The OP case is the OP case. @StringJunky is not likely to swell and crinkle when the air gets a little damp I trust.

My knowledge is very limited in this area and this thread is a lesson for me on factors to consider. I very much appreciate everyone's input.

[TheVat]

Hopeful there won't be too many pissing contests in the humidity thread.

Comfort does seem very subjective, based on my experience living on a high arid steppe.  Ms Vat and I have gotten so acclimated that when we travel east to someplace like Omaha it feels like driving into a Lousiana swamp.  

The thread has prompted me to think more about getting a humidifier, for the sake of skin and mucous membranes in the winter.  Piano hygrometer was at 20 this morning.  Came up to 22 after we boiled water for oats and made coffee, so kitchen activity doesn't make a big difference.

 

[sethoflagos]

Find I have nothing I can usefully add now.

Thanks for the reps anyway.

Edited December 3, 2023 by sethoflagos

[studiot]

2 hours ago, sethoflagos said:

600W of dry heat input would make a room this size quite warm quite quickly.

I am skeptical about this. 600w is a very low powered heater and it depends upon the construction of the room and what you mean by warm.

 

[aside]

One thing I noticed about heat pumps is the impression that a source- to air  pump (ie one which drive a non electric fan heater) generates an impression of warmth much more quickly than source -to-water pumps. This also applies to electric fan heaters and fan assisted radiators.

They only heat the air and the effect dissipates very rapidly when the heat is turned off.

[swansont]

1 hour ago, sethoflagos said:

Strawman. I said no such thing.

Far from the first time you've responded in this way to my posts. Just saying.

Was “I do NOT mean 'the first bit of bs I found via google” something I imagined? 

[sethoflagos]

2 hours ago, studiot said:

I am skeptical about this. 600w is a very low powered heater and it depends upon the construction of the room and what you mean by warm.

The OP room is ~ 40 m³ air space - typical of say a medium sized British bedroom.

British bedrooms are typically not ventllated as much as they might be, especially at this time of year, but for the sake of argument let's give it the full 7 volume changes per hour: 280 m³/hr.

Air density is oto 1.2 kg/m³ for a mass flow of 336 kg/hr or 0.933 kg/s.

Air specific heat is 1,005 J/kgK for an energy flow of 93.8 W/K.

Therefore 600W dry heat input gives a room temperature of ~600/93.8 or 6.4 degrees above that of the incoming air.

Since the incoming air is likely to be preheated air from elsewhere in the house, I suspect the room will be noticeably warm by most people's standards.

Add to that the 80W or so contribution from @StringJunky's metabolism and taking the reasonable assumption that the room is not fully aired continuously, then things might be getting a bit toasty, don't you think? We're certainly well above his 15^o C upper threshold of comfort.

1 hour ago, swansont said:

Was “I do NOT mean 'the first bit of bs I found via google” something I imagined?

No

3 hours ago, swansont said:

the first couple of dozen results on Google.

You referred to in belittling my initial post are typically not

3 hours ago, swansont said:

ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) or NIST

references. They are predominantly unreliable as you implied in your original post.

You are once again being deliberately disingenuous in your argument. This is not worthy of a figure of your standing in this community.

Edited December 3, 2023 by sethoflagos
Clarification

[Phi for All]

!

Moderator Note

Folks, let's not take professional disagreement personally. The science can be discussed without hurt feelings, can't it? I've read this thread through twice now and don't see anything other than disagreement, no vendettas or obsessions. Please carry on.

 

[studiot]

18 minutes ago, sethoflagos said:

The OP room is ~ 40 m³ air space - typical of say a medium sized British bedroom.

British bedrooms are typically not ventllated as much as they might be, especially at this time of year, but for the sake of argument let's give it the full 7 volume changes per hour: 280 m³/hr.

Air density is oto 1.2 kg/m³ for a mass flow of 336 kg/hr or 0.933 kg/s.

Air specific heat is 1,005 J/kgK for an energy flow of 93.8 W/K.

Therefore 600W dry heat input gives a room temperature of ~600/93.8 or 6.4 degrees above that of the incoming air.

Since the incoming air is likely to be preheated air from elsewhere in the house, I suspect the room will be noticeably warm by most people's standards.

Add to that the 80W or so contribution from @StringJunky's metabolism and taking the reasonable assumption that the room is not fully aired continuously, then things might be getting a bit toasty, don't you think? We're certainly well above his 15^o C upper threshold of comfort.

 

6.4C above incoming ?

SJ was looking for 14C

 

On 11/30/2023 at 9:24 PM, StringJunky said:

My portable dehumidifier is a desiccant type. The air that comes out is probably 3 or 4c higher in a 15' x 10' space. Consumption is 600w. Would 600w be fairly economical to makew the space what I call autumnal temperature; 14c. I  find it striking that people go through Autumn here with no heating, then come the proper cold, they whack  it up 6c higher or more than they were happy with the prior two months.

 

That copes incoming air 7.6C  or above.

Currently the air outside has risen from 0C first thing this morning to 7C now.

Perhaps that explains why what most estate agents in the UK would call a good sized double bedroom that tend to have 2.5kw wet radiators these days.

Yes you could get preheated air from somwhere else and then you might get away with a smaller heater, but of course you would need another heater to preheat it.

[sethoflagos]

5 minutes ago, studiot said:

6.4C above incoming ?

SJ was looking for 14C

Yes, but his 'incoming' was 10^oC so 600W is more than enough for him for that room.

 

9 minutes ago, studiot said:

Perhaps that explains why what most estate agents in the UK would call a good sized double bedroom that tend to have 2.5kw wet radiators these days.

I guess we're both old enough to remember unheated bedrooms with ice on the inside of the windows. Mine became a town centre car park in the 70's.

[StringJunky]

1 hour ago, sethoflagos said:

Yes, but his 'incoming' was 10^oC so 600W is more than enough for him for that room.

 

I guess we're both old enough to remember unheated bedrooms with ice on the inside of the windows. Mine became a town centre car park in the 70's.

Yes, 4c above an ambient of 10c. One of the joys of single-planed windows was 'Jack  Frost's' work on them in the 60's and 70's. My earliest memory was tiptoeing on the stones laid in grass to the toilet (outhouse) at the end of the garden and relieving my bladder on iced water. Bath times were in front of the fire in a galvanized tin bath in the winter,  otherwise it was in the square ceramic sink where Mum did the washing. Kitchen was a single-paned 'conservatory' extension with red tiles laid on dirt. Fun times.,

[sethoflagos]

47 minutes ago, StringJunky said:

Yes, 4c above an ambient of 10c. One of the joys of single-planed windows was 'Jack  Frost's' work on them in the 60's and 70's. My earliest memory was tiptoeing on the stones laid in grass to the toilet (outhouse) at the end of the garden and relieving my bladder on iced water. Bath times were in front of the fire in a galvanized tin bath in the winter,  otherwise it was in the square ceramic sink where Mum did the washing. Kitchen was a single-paned 'conservatory' extension with red tiles laid on dirt. Fun times.,

This is the York Marygate I remember from the early '60s. I'm not sure top left actually is Walker Street (during 'slum' clearance), as they were all very similar.

I

We were right by the river and I do remember being flooded out a couple of times. A bit of an inconvenience, but the area had more character than you can easily find these days.