The investment arm of Kuwait’s social security system bought a luxury apartment building in Manhattan’s Noho neighborhood, as demand for multifamily properties surges, two people with knowledge of the deal said.

Wafra Investment Advisory Group Inc. completed the purchase of 2 Cooper Square, a 144-unit building that includes a rooftop pool, video-game center and private movie-screening room, said the people, who didn’t disclose the price and asked not to be named because the transaction hasn’t been made public. The owner was Atlantic Development Group LLC, a Manhattan-based builder that completed the tower in 2010, according to the property’s website.

The dollar volume of Manhattan apartment sales more than doubled in 2011 from the previous year to $4.58 billion, data from Real Capital Analytics Inc. in New York show. About 195 properties changed hands, up 43 percent from 2010. Manhattan apartment investors paid an average of $456,796 per unit last year, up 57 percent from 2010. Nationally, multifamily investors paid about $101,925 per unit, Real Capital said.

Edward Ryan, a Wafra representative in New York, declined to comment on the Cooper Square deal. Julie Halpin, a spokeswoman for Atlantic Development, didn’t immediately respond to an e-mail and telephone message seeking comment today. The broker on the deal, Doug Harmon, senior managing director at Eastdil Secured LLC, didn’t immediately return a phone call today. Neither did Martha Wallau, a spokeswoman for Eastdil.

UDR Purchase

The purchase is the second in the past two weeks of a new rental apartment property in Manhattan. On Jan. 12, UDR Inc. (UDR), the third-largest publicly traded U.S. apartment owner, and MetLife Inc. said they bought a five-tower apartment complex on Manhattan’s Upper West Side for about $630 million.

The median effective rent for Manhattan apartments, or what tenants paid after landlord-sponsored incentives, rose 9.5 percent in the fourth quarter from a year earlier to $3,121 a month, appraiser Miller Samuel Inc. and broker Prudential Douglas Elliman Real Estate said in a Jan. 12 report.

At 2 Cooper Square, available one-bedroom apartments rent for as much as $6,686 a month, according to the property’s website. A two-bedroom unit is listed for $9,335 a month, while a four-bedroom apartment commands $22,000 a month.