Greetings, Doug,
 
Having lived for nearly 40 years in New England, in coastal MA, coastal and central NH (including near Concord), and north central CT currently, I am not clear on your temperatures.  During the warm weather, temperatures "peaking in the high 60s" would be the lows.  Highs generally are in the 80s, with some lower and some higher.  Winter Ts "bottoming out in the low 30s" would be the highs.  Lows in the winter generally are in the teens, with plenty of lows in the single digits and a handful below zero, and occasionally lows in the 20s.  There have been many stretches of weeks where the Ts have never gone above freezing.  In my current location in CT, which is considered southern NE, average July highs are 85, with average lows of 63.  Average highs for January are 34 with average lows of 18.  For concord, NH, averages are July 82/58 and January 31/10.  So perhaps you could further explain what you mean by your numbers.  Thanks!
 
Marc 

From: Douglas Nishimura
Sent: Friday, July 14, 2017 6:59 PM
To: [log in to unmask]
Subject: [MUSEUM-L] HVAC in New England.

Mr. Hosley. I needed a bit of time to see what I was dealing with so I’m a bit slow to respond to your reply from last week. At least we’ve isolated the condition down to New England like climate and the condition that it depends on what you have stored. So the original statement really isn’t a general statement about the value of HVAC for all materials in all places.

 

Not being familiar with New England climates, I had a look at the last three years of outdoor climate data from Noaa for some more or randomly selected locations (although I did intentionally try to cover as many states as I could in my selection.) So I looked at Nantucket, Bennington, Portland, Concord, and New Haven. I have to admit that I was quite surprised at how similar the data was.

 

Temperatures were generally pretty moderate peaking mostly in the high 60s  (19 or 20 C – ish) so for materials that tolerate room temperature//human comfort temperatures, it really isn’t bad, although there were days into the high 80s and even almost 100  F (around 37 C. I’m not sure how international this list membership is, but Si units are included for the non-Americans.) So some cooling is needed, but as you point out, probably not needing as much as we might in a place like upstate New York.

 

At the other end, winters bottom out in the low 30s (around +1 or +2 C) and for about five months in each of the three years of data, the temperature was below 35 F (+2 C) so winter heating is probably necessary..

 

All year round, the outdoor humidities sit around the very high 60s (68%, 69%) to mid-70s %. Between the end of the heating season and the start of the next, humidity control will be an issue.

 

The dew point temperature changes quite rapidly between the summer and winter. In all five locations and three years,  the dew point temperature reaches about 55 F (13C) around the beginning of June and sits at a peak between about 65 F (18 C) and 69 F (21 C) for about three months before finally dropping below 55 F ( 13 C) around the end of September. All other things being equal, a dew point temperature of 55 F (13 C) will produce a humidity of about 59%  at 70 F (21 C). The peak dew point  produces a humidity between about 84% and 93% RH.

 

Cooling could bring down the humidity, but every small air conditioner that I’ve ever looked at (and even my central air conditioner at home) all work on thermostatic control while a New England institution is less likely to require cooling, but needs dehumidification. It’s possible that a compromise might be reached by using dehumidifiers, although they add to the heat load that needs to be removed along with heat generated by people and lights. Opening windows to bring down the heat load brings up the humidity so monitoring and testing is required to find an appropriate compromise if one wants to avoid installing a “large and invasive” system.

 

Around mid-November, the dew point temperature drops below 35 F (2 C) and stays below there through to May. Ignoring the up and down spikes, the dew point tends to sit between about 15 F and 20 F (about -7 C and -9 C).

 

Heating the building to about 70 F (21 C), would leave the humidity at about 11% to 14% RH for about three months so occupied buildings require winter humidification.

 

Rick Kerschner has gotten around this by allowing buildings to be minimally heated leaving them around 40 F (+4 C) for the winter. However, this approach has several conditions: The building can’t be occupied (or occupants are willing to wear winter clothing indoors), there can’t be plumbing in the building or it must be possible to drain it for winter, and finally museum objects in the building must tolerate the colder temperatures.

 

Humidification is also required for the winter if the existing conditions don’t allow the low winter heating option to be used.

 

Even in New England, HVAC can’t be completely dismissed, but there may be lower cost solutions depending on the size of the institution, how it operates, the design and construction of the buildings and collection objects housed there.

 

-Doug

Douglas Nishimura

Image Permanence Institute

Rochester Institute of Technology

 


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